Solid polymer electrolyte, a membrane using thereof, a solution for coating electrode catalyst, a membrane/electrode assembly, and a fuel cell

ABSTRACT

It is an object of the present invention to provide  
     It is an object of the present invention to provide an easy manufacturability high-durability solid polymer electrolyte, a solid polymer electrolyte membrane using thereof, a solution for covering electrode catalyst, a membrane/electrode assembly, and a fuel cell.  
     The method in accordance with the present invention directly bonds a sulfonic group to an aromatic ring of aromatic hydrocarbon polymer with an alkyl group therebetween. The present invention can provide solid polymer electrolytes, solid polymer electrolyte membranes using thereof, solutions for covering electrode catalyst, membrane/electrode assemblies, and fuel cells, causing the products to have greater ion conductivities than aromatic hydrocarbon polymers which have sulfonic groups directly bonded to aromatic rings, to suppress sulfonic groups from being dissociated at a high temperature in the presence of a strong acid, and to show a substantially high chemical durability.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a low-cost high-durability andhigh oxidation-resistant solid polymer electrolyte fit for anelectrolyte membrane used for fuel cells, electrolysis of water,electrolysis of halogenated hydracid, electrolysis of salt (solution),oxygen concentrators, humidity sensors, and gas sensors, a solid polymerelectrolyte membrane using thereof, a solution for covering electrodecatalyst, a membrane/electrode assembly, and a fuel cell.

[0002] A solid polymer electrolyte is a solid polymer material havingelectrolytic groups such as sulfonic groups in polymer chains and hasfeatures of strongly bonding to specific ions and selectively permeatingcations or anions. The solid polymer electrolyte is formed intoparticles, fibers or thin films and used for electrodialysis, diffusiondialysis, cell diaphragms, and so on.

[0003] A reformed gas fuel cell comprising a cathode, an anode, and aproton conducting solid polymer electrolyte membrane sandwiched betweenthese electrodes supplies a hydrogen gas obtained by reforminghydrocarbons of low molecular weights such as methane and methanol as afuel gas to one electrode (fuel electrode) and an oxygen gas or air asan oxidizing agent to the other electrode (air electrode), and obtainselectromotive forces by their reactions. Electrolysis of waterelectrically decomposes water by a solid polymer electrolyte membraneinto hydrogen and oxygen.

[0004] Fluorine-related electrolyte membrane such as perfluorocarbonsulfonic membrane having high proton conducting show very high long-termchemical stability as a solid polymer electrolyte membrane for fuelcells and water electrolysis. Typical products of the fluorine-relatedelectrolyte membrane are Nafion (trademark of DuPont), Aciplex(trademark of Asahi Chemicals Co., Ltd.) and Flemion (trademark of AsahiGlass Co., Ltd.)

[0005] Electrolysis of a salt solution electrically decomposes a watersolution of sodium chloride by a solid polymer electrolyte membrane intosodium hydroxide, chlorine, and hydrogen. As the solid polymerelectrolyte membrane. In this case, the electrolyte membrane is incontact with a chlorine gas and a hot and concentrated water solution ofsodium chloride and must be resistant to them. Thereforehydrocarbon-related electrolyte membranes are not available. In general,perfluorocarbon sulfonic membranes having carboxylic groups partially onits surface to prevent inverse diffusion of ions are used as solidpolymer electrolyte membranes which is resistant to chlorine gas and hotand concentrated alkaline water.

[0006] Basically, the fluorine-related electrolyte represented by carbonsulfonic membranes is very high chemical stability due to C—F bonds. Thefluorine-related electrolyte membranes are used not only as solidpolymer electrolyte membranes for fuel cells, water electrolysis, orsalt electrolysis but also as solid polymer electrolyte membranes forelectrolysis of halogenated hydracid. Due to its high proton conducting,the fluorine-related electrolyte membranes are also used for humiditysensors, gas sensors, oxygen concentrators, and so on.

[0007] Contrarily, the fluorine-related electrolyte membranes are hardto be manufactured and very expensive. So their use is much limited forexample, to solid polymer electrolyte fuel cells for space and militaryfields and to other particular uses. They are hard to be used for solidpolymer electrolyte fuel cells as low-pollution power sources forautomobiles and other public uses.

[0008] So various aromatic hydrocarbon electrolyte membranes asinexpensive solid polymer electrolyte membranes have been disclosed suchas sulfonated poly-ether ether ketone by Japanese Non-examined PatentPublications No.H06-93114 (1994), sulfonated poly-ether sulfone JapaneseNon-examined Patent Publications No.H09-245818 (1997) and JapaneseNon-examined Patent Publications No.H11-116679 (1999), sulfonatedacrylonitrile butadiene styrene monomer by Japanese Non-examined PatentPublications No.H10-503788 (1998), sulfonated poly sulfide by JapaneseNon-examined Patent Publications No.H11-510198 (1999), and sulfonatedpolyphenylene by Japanese Non-examined Patent Publications No.H11-515040(1999). The aromatic hydrocarbon electrolyte membranes prepared bysulfonating engineer plastics are easier to be manufactured and lowercosted than fluorine-related electrolyte membranes represented byNafion. However, one of the demerits of the aromatic hydrocarbonelectrolyte membranes is to be easily deteriorated. This reason isrevealed by Japanese Non-examined Patent Publications No.2000-106203. Itsays the main reason is that the structure of aromatic hydrocarbon isoxidized and broken by hydrogen peroxide which generates in the catalystlayer on the boundary between the solid polymer electrolyte membrane,and the air electrode (oxidant electrode).

[0009] So various trials have been made to prepare a solid polymerelectrolyte which is as resistant to oxidation as the fluorine-relatedelectrolyte membrane or stronger and which can be manufactured at lowcosts. For example, Japanese Non-examined Patent PublicationsNo.H09-102322 (1997) proposes a membrane made of sulfonic typepolystyrene graft ethylenetetrafluoroethylene (ETFE) co-polymer having ahydrocarbon-related side chain and a main chain formed bycopolymerization of fluorinecarbide-related vinyl monomer andhydrocarbon related vinyl monomer. This polystyrene-graft-ETFE membrane(aromatic hydrocarbon polymer) is not expensive and strong enough as asolid polymer electrolyte membrane for fuel cells. Its conductivity canbe improved by increasing the quantity of sulfonic groups to beattached. However, the side chains of this membrane having sulfonicgroups are easily subject to deterioration by oxidation although themain chains formed by copolymerization of fluorinecarbide-related vinylmonomer and hydrocarbon related vinyl monomer. Therefore, thispolystyrene-graft-ETFE membrane as a total is not resistant to oxidationand not so durable. Consequently, this polystyrene-graft-ETFE membraneis not available to fuel cells.

[0010] U.S. Pat. No. 4,012,303 and U.S. Pat. No. 4,605,685 propose asulfonic poly-(trifluorostyrene) graft ETFE polymer electrolyte membranewhich is prepared by copolymerizing fluorinecarbide-related vinylmonomer and hydrocarbon related vinyl monomer, grafting α, β,β-trifluorostyrene with the resulting membrane, and attaching sulfonicgroups thereto. This membrane uses α, β, β-trifluorostyrene which ispartially fluorined instead of styrene because the polystyrene sidechain having sulfonic groups is not chemically stable. However, it isvery difficult to synthesize α, β, β-trifluorostyrene which is materialof the side chains. Further, the material as well as Nafion is tooexpensive to be used as solid polymer electrolyte membranes for fuelcells. Furthermore, α, β, β-trifluorostyrene has low reactivity ofpolymerization and consequently the quantity of α, β, β-trifluorostyreneto be grafted for side chains is very small. The conductivity of theresulting membrane is very low.

[0011] It is an object of the present invention to provide an easymanufacturability high-durability solid polymer electrolyte which is asdurable as the fluorine-related electrolyte or has substantially highchemical stability, a solid polymer electrolyte membrane using thereof,a solution for covering electrode catalyst, a membrane/electrodeassembly, and a fuel cell.

SUMMARY OF THE INVENTION

[0012] To dissolve the aforesaid problems, we inventors researched themechanism of deterioration of electrolyte membranes and found that themain cause of the deterioration of the aromatic hydrocarbon electrolytemembranes is not the deterioration by oxidation but rather the directbonding of a sulfonic group to an aromatic ring. This direct bondingallows the sulfonic group to be easily cut out from the aromatic ring inthe presence of a strong acid at a high temperature and as the result,causes reduction of its ionic conductivity. Judging from this result,the high-durability solid polymer electrolyte in accordance with thepresent invention is an aromatic hydrocarbon polymer having a sulfoalkylgroup (FORMULA 1) instead of a sulfonic group in the side chain. Thepresent invention can provide low-cost high durability solid polymerelectrolyte which is as durable as the fluorine-related electrolyte orhas substantially high chemical stability, Further, the ionicconductivity of the electrolyte having the sulfoalkyl groups in the sidechains is greater than the ionic conductivity of the electrolyte havingthe sulfonic groups in the side chains (per weight equivalent to ionexchange group). it is assumed that is related to that the sulfoalkylgroups can move more freely than the sulfonic groups.

[0013] Said aromatic hydrocarbon polymer compound is preferablypoly-ether sulfone polymer compounds, poly ether ether kletone polymercompounds, polyphenylene sulfide polymer compounds, polyphenylene etherpolymer compounds, poly-sulfone polymer compounds, or poly ether ketonepolymer compounds.

[0014] It is preferable that the polymer electrolyte membrane and thesolution for covering electrode catalysts contain said polymerelectrolyte.

[0015] In accordance with the present invention, it is preferable that amembrane/electrode assembly for a solid polymer electrolyte fuel cellcomprises a polymer electrolyte membrane and a gas diffusion electrodeunit comprising a cathode and an anode which are placed on both sides ofsaid polymer electrolyte membrane, wherein said polymer electrolytemembrane is any polymer electrolyte membrane stated above, said gasdiffusion electrodes bind fine catalytic metal particles to the surfacesof a conductive material made of carbon with a binder, and said binderis made of any polymer electrolyte stated above.

[0016] In accordance with the present invention, it is preferable that asolid polymer electrolyte fuel cell comprise a polymer electrolytemembrane, one pair of gas diffusion electrodes comprising a cathode andan anode which are placed on both sides of said polymer electrolytemembrane, one pair of gas impermeable separators which are provided tosandwich said gas diffusion electrodes, and one pair of currentcollecting members which are placed between said solid polymer and saidseparator, wherein said solid polymer electrolyte membrane is made ofany polymer electrolyte membrane stated above and said polymerelectrolyte membrane and said gas diffusion electrodes are made of saidmembrane/electrode assembly for a solid polymer electrolyte fuel cell.

BRIED DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 shows the structure of a unit cell of a solid polymerelectrolyte fuel cell.

[0018]FIG. 2 shows the result of an endurance test of the unit cell of asolid polymer electrolyte fuel cell.

[0019]FIG. 3 is a picture showing the appearance of a 3 KW layer-builtcell (stack) integrating the unit cells for a solid polymer electrolytefuel cell.

[0020]FIG. 4 shows a relationship between current density and outputvoltage of a unit cell of a solid polymer electrolyte fuel cell.

[0021]FIG. 5 shows the result of an endurance test of the unit cell of asolid polymer electrolyte fuel cell.

[0022]FIG. 6 shows a relationship between current density and outputvoltage of a unit cell of a solid polymer electrolyte fuel cell.

[0023]FIG. 7 shows the result of an endurance test of the unit cell of asolid polymer electrolyte fuel cell.

[0024]FIG. 8 shows a relationship between current density and outputvoltage of a unit cell of a solid polymer electrolyte fuel cell.

[0025]FIG. 9 shows the result of an endurance test of the unit cell of asolid polymer electrolyte fuel cell.

[0026]FIG. 10 shows a relationship between current density and outputvoltage of a unit cell of a solid polymer electrolyte fuel cell.

[0027]FIG. 11 shows the result of an endurance test of the unit cell ofa solid polymer electrolyte fuel cell.

[0028]FIG. 12 shows a relationship between current density and outputvoltage of a unit cell of a solid polymer electrolyte fuel cell.

[0029]FIG. 13 shows the result of an endurance test of the unit cell ofa solid polymer electrolyte fuel cell.

[0030]FIG. 14 shows a relationship between current density and outputvoltage of a unit cell of a solid polymer electrolyte fuel cell.

[0031]FIG. 15 shows the result of an endurance test of the unit cell ofa solid polymer electrolyte fuel cell.

[0032]FIG. 16 shows a relationship between current density and outputvoltage of a unit cell of a solid polymer electrolyte fuel cell.

[0033]FIG. 17 shows the result of an endurance test of the unit cell ofa solid polymer electrolyte fuel cell.

[0034]FIG. 18 shows a relationship between current density and outputvoltage of a unit cell of a solid polymer electrolyte fuel cell.

[0035]FIG. 19 shows the result of an endurance test of the unit cell ofa solid polymer electrolyte fuel cell.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0036] The sulfoalkyl aromatic hydrocarbon electrolyte in accordancewith the present invention can be any as far as its side chain containssulfoalkyl groups and its main chain contains aromatic rings.

[0037] Substantially, the aromatic hydrocarbon electrolyte is anaromatic hydrocarbon polymer compound prepared by attaching a sulfoalkylgroup (represented by FORMULA 1) to engineering plastics or its polymeralloy such as poly-ether ether ketone (PEEK) having a structural unit(represented by FORMULA 2) developed by ICI Co., Ltd. (Great Britain) in1977, semi-crystalline poly-allyl ether ketone (PAEK) developed by BASF(Germany), poly-ether ketone (PEK) having a structural unit (representedby FORMULA 3) distributed by Sumitomo Chemicals Co., Ltd. and othercompanies, poly-ketone (PK) distributed by Teijin Amoco EngineeringPlastics Ltd., poly-ether sulfone (PES) having a structural unit(represented by FORMULA 4) distributed by Mitsui Chemicals Co., Ltd. andother companies, poly-sulfone having a structural unit (represented byFORMULA 5) distributed by Teijin Amoco Engineering Plastics Ltd., linearor bridged polyphenylene sulfide (PPS) having a structural unit(represented by FORMULA 6) distributed by Toray, Dainippon Ink andChemicals Inc., Tohpren Co., Ltd., Idemitsu Petrochemical Co., Ltd.,Kureha Chemical Industry Co., Ltd. and other companies, and reformedpolyphenylene ether (PPE) having a structural unit (represented byFORMULA 7) distributed by Asahi Chemical Industry Co., Ltd., Japan GEPlastics, Mitsubishi Engineering Plastics Co., Ltd. and SumitomoChemicals Co., Ltd. Among the above polymer compounds, sulfoalkyl PEEK,PAEK, PEK, PK, PPS, and PES are preferable judging from resistance tooxidation of the main chains.

[0038] (wherein “n” is 1, 2, 3, 4, 5, or 6)

[0039] Formula 3

[0040] Formula 4

[0041] Formula 5

[0042] Formula 6

[0043] Formula 7

[0044] Formula 8

[0045] (wherein “R” is a lower alkyl group such as methyl group or ethylgroup or a phenyl group)

[0046] Any sulfoalkylation method can be employed to attach sulfoalkylgroups to aromatic hydrocarbon polymer or its polymer alloy (FORMULA 1).For example, one method uses sultone (FORMULA 8) which is described inJ. Amer. Chem. Soc., 76, 5357-5360 (1954) to attach a sulfoalkyl groupto an aromatic ring.

[0047]   . . . FORMULA 8

[0048] (wherein “m” is 1 or 2.)

[0049] Another method takes the steps of substituting a hydrogen atom ofan aromatic ring by lithium, substituting lithium by a halogenoalkylgroup by dihalogenoalkane, and converting the halogenoalkyl group into asulfoalkyl group. A further method comprises the steps of attaching ahalogenobutyl group to an aromatic ring by a tetramethylenehalogeniumion and substituting the halogen atom by a sulfonic group. See FORMULA9.

[0050] Formula 10

[0051] The present invention does not limit a method of sulfoalkylatingan aromatic hydrocarbon polymer compound, but a method represented byFORMULA 8 is preferable judging from cost reduction.

[0052] The equivalent weight of ion exchange group of the polymerelectrolyte (that is, sulfoalkylated polymer) in accordance with thepresent invention is 250 g/mol to 2500 g/mol, preferably 300 g/mol to1500 g/mol, more preferably 350 g/mol to 1000 g/mol. If the equivalentweight of ion exchange group exceeds 2500 g/mol, the output performancewill reduce and if it falls below 250 g/mol, the water-resistance ofsaid polymer will reduce. These are not preferable.

[0053] The equivalent weight of ion exchange group in the presentinvention represents a molecular weight of said sulfoalkylated polymerper sulfoalkyl group. Smaller equivalent weight indicates higher degreeof sulfoalkylation. The equivalent weight of ion exchange group can bemeasured by ¹H-NMR spectroscopy, elementary analysis, acid-basetitration or non-aqueous acid-base titration stated in Japan PatentPublication H01-52866 (1989) (using a benzene methanol solution ofpotassium methoxide as the normal solution).

[0054] The equivalent weight of ion exchange group of the sulfoalkylatedpolymer can be controlled to be in the range of 250 g/mol to 2500 g/molby selecting a compounding ratio of aromatic hydrocarbon polymer andsulfoalkylating agent, a reaction temperature, a reaction time, achemical structure of the aromatic hydrocarbon polymer.

[0055] The polymer electrolyte in accordance with the present inventionis usually used in a form of membrane in a fuel cell. Any method can beused to form a sulfoalkylated polymer membrane. Typical forming methodsare a solution casting method which forms a membrane from a polymersolution and a molten pressing or extruding method which forms amembrane from a molten polymer. In details, the solution casting methodcomprises the steps of spreading a polymer solution over a glass plateand removing its solvent. The solvent can be any as far as it dissolvesthe polymer and is easily removed from the polymer. Preferable solventsare non-proton polar solvent such as N,N′-dimethylformamide,N,N-dimethylacetoamide, N-methyl-2-pyrolidone, and dimethylsulfoxide,

[0056] Alkylene glycol such as ethylene glycol mono-methylether,ethylene glycol mono-ethylether, propylene glycol mono-methylether, andpropylene glycol mono-ethylether, halogen solvent

[0057] The thickness of said polymer electrolyte membrane can be any butpreferably 10 μm to 200 μm and more preferably 30 μm to 100 μm. Themembrane is preferably thicker than 10 μm to be strong enough for actualuses and thinner than 200 μm to reduce the resistance of the membrane,that is, to increase the power generation performance. The solutioncasting method can control the thickness of the membrane by selecting aconcentration of the polymer solution or thickness of the polymersolution spread over a substrate. The thickness of a membrane sheet madeby the molten pressing or extruding method can be controlled by rollingat a preset rate.

[0058] When the electrolyte in accordance with the present invention ismanufactured, additives such as plasticizer, stabilizer, and partingagent can be added to the electrolyte without departing from the spiritand scope of the invention.

[0059] The gas diffusion electrodes used for a membrane/electrodeassembly in a fuel cell are made of conductive materials carryingcatalyst metal particles on them. The gas diffusion electrodes cancontain water repellent and/or binding agent if necessary. It ispossible to position, outside the catalyst layer, a layer comprising aconductive material without a catalyst and a water repellent and/orbinding agent if necessary. Catalytic metals available to the gasdiffusion electrodes can be any as far as they accelerate oxidationreaction of hydrogen and reduction reaction of hydrogen. Such metals areplatinum, gold, silver, palladium, iridium, rhodium, ruthenium, iron,cobalt, nickel, chromium, tungsten, manganese, vanadium, or theiralloys. Among these catalysts, platinum is used in most cases. Usually,the sizes of catalytic metals are 10 angstroms to 300 angstroms. Thesecatalysts are preferably deposited on carriers such as carbon, reducingthe quantity of catalysts to be used and material costs. The preferableamount of catalyst to be carried by the carrier is 0.01 mg/cm² to 10mg/cm².

[0060] The conductive material can be any as far as it is electronconductive such as metals and carbon materials. The preferable carbonmaterials are carbon black (such as furnace black, channel black, andacetylene black), active carbon, graphite, and so on. These carbonmaterials are used singly or in combination. For example, fluorocarbonis used as a water repellent. As for a binder, it is preferable to usethe solution for covering the electrode catalysts in accordance with thepresent invention judging from a point of view of bonding property, butother resins can be used as the binder. In such a case, a preferablebinder is a fluoro resin having a water-repellent property and moreparticularly has excellent heat-resistance and oxidation-resistance.Such resins are poly-tetrafluoroethylene,tetrafluoroethylene-perfluoroalkylvinylether copolymer, andtetrafluoroethylene-hexafluoropropylene copolymer.

[0061] Further, an electrolyte membrane and an electrode assemblingmethod for a fuel cell are not limited here and any prior method can beused. One method of manufacturing a membrane/electrode assemblycomprises for example the steps of adding platinum catalyst powdercarried by carbon into a polytetrafluoroethylene suspension, spreadingthe mixture over a piece of carbon paper, heat-treating the paper toform a catalyst layer, spreading an electrolyte solution which is thesame as the electrolyte membrane over the catalyst layer, andhot-pressing the electrolyte membrane and the catalyst layer in a body.The other methods are a method of coating platimum catalyst powder inadvance with an electrolyte solution which is the same as theelectrolyte membrane, a method of applying a catalyst paste onto theelectrolyte membrane, a method of electroless-plating an electrode onthe electrolyte membrane, and a method of causing the electrolytemembrane to absorb complex ions of a platinum group and reducingthereof.

[0062] A solid polymer electrolyte fuel cell piles up a plurality ofunit cells each of which consists of a membrane/electrode assembly(comprising an electrolyte membrane and gas diffusion electrodes) andouter plates (a grooved fuel distributing plate having fuel paths and agrooved oxidant distributing plate having oxidant paths) which also workas current collectors with a cooling plate between the cells. It ispreferable to operate a fuel cell at a higher temperature. This isbecause the activity of the electrode catalyst increases and as theresult overvoltages on the electrodes reduce at a high temperature.However, as the electrolyte membrane cannot work without water, theoperating temperature of the fuel cell must be such that the water maybe controlled. Therefore, the preferable operating temperature of thefuel cell is between a room temperature and 100° C.

[0063] The present invention will be explained in more detail from thefollowing description of embodiments. It is to be expressly understood,however, that the embodiments are for purpose of explanation only andare not intended as a definition of the limits of the invention. Theconditions of measuring respective properties are as follows:

[0064] [Ion Exchange Group Equivalent Weight]

[0065] We took an exact weight (“a” gram) of sample sulfoalkylatedpolymer in a glass container which could be tightly sealed, added anexcessive calcium chloride aqueous solution to the content of the glasscontainer, stirred the content for one night, and titrated hydrogenchloride which generated in the glass container with a 0.1N standardaqueous solution of sodium hydroxide (potency: f) by using aphenolphthalein indicator (“b” ml). The Ion exchange group equivalentweight (g/mol) was calculated by

[0066] Ion exchange group equivalent weight=(1000×a)/(0.1×b×f)

[0067] (2) Evaluation of Output Performance of a Unit Cell of the FuelCell

[0068] We set an electrolyte bonded with electrodes in a sample unitcell and measured the output performance of the unit cell.

[0069] We supplied hydrogen gas and oxygen gas at one atmosphericpressure to the sample unit cell through a water bubbler (at 23° C.) tohumidify the gases. The flow rates of the hydrogen gas and the oxygengas are respectively 60 ml/min (for hydrogen) and 40 ml/min (foroxygen). The temperature of the cell is 70° C. We measured the outputperformance of the cell by the H201B charging/discharging unit (HokutoDenko Co., Ltd.).

[0070] [Embodiment 1]

[0071] (1) Preparation of Sulfopropyl Polyether Sulfone

[0072] We prepared sulfopropyl polyether sulfone by setting up a 500-ml4-neck round bottom flask with a reflux condenser, a stirrer, athermometer, and a desiccant tube (containing calcium chloride in it),substituting the air inside the flask by nitrogen gas, putting 21.6 g ofpolyethersulfone (PES), 12.2 g (0.1 mol) of propansultone and 50 ml ofdry nitrobenzene in the flask, adding 14.7 g (0.11 mol) of aluminumchloride anhydride to the mixture gradually for 30 minutes whilestirring thereof, refluxing the mixture for 8 hours after addition ofaluminum chloride anhydride is completed, adding 500 ml of iced watercontaining 25 ml of concentrated hydrochloric acid to the reactant tostop the reaction, dripping the reactant solution slowly into 1 liter ofdeionized water, filtering the deionized water to recover theprecipitate (sulfopropyl polyethersulfone), repeating mixing theprecipitate with deionized water and suction-filtering the mixture untilthe filtrate becomes neutral, and vacuum-drying the precipitate at 120°C. for one night. The ion exchange group equivalent weight of theobtained sulfopropyl polyethersulfone is 980 g/mol.

[0073] The cost of the sulfopropyl polyethersulfone electrolyte is onefiftieth of the cost of perfluorosulfonic electrolyte which is preparedfrom expensive material in five processes because the sulfopropylpolyethersulfone electrolyte is prepared in a single process frompoly-ether sulfone which is very cheap engineering plastics on-market.

[0074] We put 1.0 g of obtained sulfopropyl polyethersulfone and 20 mlof deionized water in a Teflon-coated hermetic stainless steelcontainer, kept the container at 120° C. for 2 weeks, cooled thecontainer and then measured the ion exchange group equivalent weight ofsulfopropyl polyethersulfone. As the result, we found that the ionexchange group equivalent weight of sulfopropyl polyethersulfone remainsunchanged (980 g/mol) and that sulfopropyl polyethersulfone is as stableas the expensive perfluorosulfonic electrolyte. Contrarily as shown bythe comparative example1 below, the cheap sulfonated aromatichydrocarbon electrolyte is deteriorated under the same temperature andhydrolysis condition. Its ion exchange group equivalent increases up to3,000 g/mol (which was initially 960 g/mol) and sulfone groups weredissociated. In other words, the low-cost sulfopropyl polyethersulfoneelectrolyte unlike the cheap sulfonated aromatic hydrocarbon electrolyte(see Comparative example 1) shows very good chemical stability as wellas the expensive perfluorosulfonic electrolyte, satisfying both low costand high performance.

[0075] (2) Preparation of an Electrolyte Membrane

[0076] We prepared an electrolyte membrane by dissolving the productobtained by the above description (1) into a mixture of 20 parts ofN,N′-dimethylformamide, 80 parts of cyclohexanon, and 25 parts ofmethylethylketone so that the solution may contain 5% by weight of theproduct, spreading this solution over a glass plate by spin-coating,air-drying thereof, and vacuum-drying thereof at 80° C. The obtainedelectrolyte membrane I is 42 μm thick and its ion exchange groupequivalent is 5 S/cm.

[0077] We put said obtained electrolyte membrane I and 20 ml ofdeionized water in a Teflon-coated hermetic stainless steel container,kept the container at 120° C. for 2 weeks, cooled the container and thenmeasured its ion exchange group equivalent weight. As the result, wefound that the ion exchange group equivalent weight of the obtainedelectrolyte membrane remains unchanged as well as the expensiveperfluorosulfonic electrolyte. The membrane itself is tough enough.Contrarily as shown by the comparative example 1-(2), the comparativelycheap sulfonated aromatic hydrocarbon electrolyte II is broken andragged under the same temperature and hydrolysis condition. In otherwords, the low-cost sulfopropyl polyethersulfone electrolyte unlike thecheap sulfonated aromatic hydrocarbon electrolyte (see Comparativeexample 1-(2)) shows very good chemical stability as well as theexpensive perfluorosulfonic electrolyte, satisfying both low cost andhigh performance.

[0078] (3) Preparation of a Solution for Covering Electrode Catalyst anda Membrane/Electrode Assembly

[0079] We prepared a solution I for covering electrode catalyst byadding a solvent mixture of N,N′-dimethylformamide, cyclohexanon, andmethylethylketone which contains 5% by weight of the product (see (2))to carbon carrying 40% by weight of platinum so that the ratio by weightof platinum catalyst and the polymer electrolyte might be 2:1, anddispersing the mixture uniformly. Next we prepared a membrane/electrodeassembly I by coating both sides of the electrolyte membrane I (obtainedby (2)) with said solution I for covering electrode catalyst, and dryingthereof. The obtained membrane/electrode assembly I carries 0.25 mg/cm²of platinum.

[0080] Similarly we prepared a membrane/electrode assembly I′ carrying0.25 mg/cm² of platinum by coating both sides of the electrolytemembrane I (obtained by (2)) with said solution II for coveringelectrode catalyst stated by Comparative example 1 (2), and dryingthereof.

[0081] We prepared a paste (a solution for covering electrode catalystby adding an alcohol-water mixture of 5% by weight as perfluorocarbonsulfonic electrolyte to carbon carrying 40% by weight of platinum sothat the ratio by weight of platinum catalyst and the polymerelectrolyte might be 2:1, and dispersing the mixture uniformly. Next wecoated both sides of the electrolyte membrane I (obtained by (2)) withthis paste (solution). However, the paste could not be uniformly spreadover the electrolyte membrane and we could not get a membrane/electrodeassembly. Therefore, the solution I is superior as a solution forcovering electrode catalysts.

[0082] We put said obtained membrane/electrode assembly I and 20 ml ofdeionized water in a Teflon-coated hermetic stainless steel container,kept the container at 120° C. for 2 weeks, cooled the container and thenmeasured its ion exchange group equivalent weight.

[0083] As the result, we found that the ion exchange group equivalentweight of the obtained electrolyte membrane remains unchanged as well asthe membrane/electrode assembly prepared from the expensiveperfluorosulfonic membrane and the perfluorosulfonic electrolyte. Themembrane itself is tough enough.

[0084] Similarly, we put said obtained membrane/electrode assembly I′and 20 ml of deionized water in a Teflon-coated hermetic stainless steelcontainer, kept the container at 120° C. for 2 weeks, cooled thecontainer and then measured its property.

[0085] As the result, we found that the membrane/electrode assembly I′has enough power generating performance although the electrode waspartially separated.

[0086] Contrarily as shown by the comparative example1 (3), themembrane/electrode assembly II prepared by comparatively cheapsulfonated aromatic hydrocarbon electrolyte II and the electrodecatalyst covering solution II is broken and ragged under the sametemperature and hydrolysis condition. In other words, the low-costsulfopropyl polychlorofluoroethylene membrane/electrode assembly unlikethe cheap sulfonated aromatic hydrocarbon electrolyte membrane (seeComparative example 1 (3) is as stable as the expensiveperfluorosulfonic membrane/electrolyte assembly, and satisfies both lowcost and high performance.

[0087] (4) Endurance test of unit cells of a fuel cell We evaluated theoutput performance of fuel cells by dipping said membrane/electrodeassembly I and I′ in deionized boiling water to let the assemblis absorbwater and setting each wet membrane/electrode assembly in a sample unit.FIG. 1 shows the structure of the sample unit cell of the solid polymerelectrolyte fuel cell which comprises said membrane/electrode assembly 4which is prepared by (3) and made up with a polymer electrolyte membrane1, an oxygen electrode 2 and an hydrogen electrode 3, current collectingmembers 5 which are supported and sealed by thin packing material madeof carbon paper on the electrodes, and conductive separators 6 (bipolarplates) provided on outer sides of the current collecting members 5 toseparate electrodes from the chamber and to supply gasses. The oxygenelectrode 2 works as a cathode and the hydrogen electrode 3 works as ananode.

[0088] We measured the output voltage of said unit cell of the solidpolymer electrolyte fuel cell while running the unit cell for a longtime at a current density of 300 mA/cm². FIG. 2 shows the relationshipbetween the output voltage and the running time of the unit cell. Thecurve 12 in FIG. 2 is the result of the endurance test of the unit cellusing the membrane/electrode assembly I in accordance with the presentinvention. The curve 13 in FIG. 2 is the result of the endurance test ofthe unit cell using the membrane/electrode assembly I′. The curve 14 inFIG. 2 is the result of the endurance test of the unit cell using aperfluorosulfonic membrane/electrode assembly. As shown by curve 12 inFIG. 2, the output voltage of the membrane/electrode assembly I isinitially 0.8 V and keeps at 0.8 V even after the unit cell runs 5,000hours, which is the same as the behavior of the output voltage of theunit cell using a perfluorosulfonic membrane/electrode assembly (bycurve 14). As shown by curve 15 in FIG. 2, the output voltage (of a unitcell using sulfonated aromatic hydrocarbon electrolyte of Comparativeexample 1 below) is initially 0.73 V but completely exhausted after thefuel cell runs 600 hours. Judging from these, it is apparent that theunit cell of a fuel cell using an aromatic hydrocarbon electrolytehaving a sulfonic group bonded to the aromatic ring via an alkyl groupis more durable than the unit cell of a fuel cell using an aromatichydrocarbon electrolyte having a sulfonic group directly bonded to thearomatic ring. Further, although both membrane/electrode assemblies ofEmbodiment 1 and Comparative example 1 carry 0.25 mg/cm² of platinum,the output voltage of Embodiment 1 is greater than the output voltage ofComparative example 1. This is because the ion conductivities of theelectrolyte and the electrode catalyst covering solution in themembrane/electrode assembly of Embodiment 1 are greater than those ofthe electrolyte and the electrode catalyst covering solution in themembrane/electrode assembly of Comparative example 1 and because themembrane/electrode assembly of Embodiment 1 is superior to themembrane/electrode assembly of Comparative example 1.

[0089] (5) Preparation of Fuel Cells

[0090] We piled up 36 unit cells which were prepared in (4) to form asolid polymer electrolyte fuel cell. This fuel cell outputs 3 KW.

COMPARATIVE EXAMPLE 1

[0091] (1) Preparation of Sulfonated Polyether Sulfone

[0092] We prepared sulfonated polyether sulfone by setting up a 500-ml4-neck round bottom flask with a reflux condenser, a stirrer, athermometer, and a desiccant tube (containing calcium chloride in it),substituting the air inside the flask by nitrogen gas, putting 25 g ofpolyethersulfone (PES) and 125 ml of concentrated sulfuric acid in theflask, stirring the mixture at a room temperature for one night in thepresence of nitrogen gas to make a uniform solution, dripping 48 ml ofchlorosulfuric acid first slowly (because the chlorosulfuric acidvigorously reacts with water in the sulfuric acid with bubbles) by adropping funnel into the uniform solution in the presence of nitrogengas, completing dripping within 5 minutes after bubbling calms down,stirring the reactant solution at 25° C. for three and half hours tosulfonate thereof, dripping the reactant solution slowly into 15 litersof deionized water, filtering the deionized water to recover theprecipitate (sulfonated poly-ethersulfone), repeating mixing theprecipitate with deionized water and suction-filtering the mixture untilthe filtrate becomes neutral, and vacuum-drying the precipitate at 80°C. for one night. The ion exchange group equivalent weight of theobtained sulfonated poly-ethersulfone electrolyte is 960 g/mol.

[0093] We put 1.0 g of obtained sulfonated polyethersulfone electrolyteand 20 ml of deionized water in a Teflon-coated hermetic stainless steelcontainer, kept the container at 120° C. for 2 weeks, cooled thecontainer and then measured the ion exchange group equivalent weight ofsulfonated polyethersulfone. As the result, we found that the ionexchange group equivalent weight of sulfonated polyethersulfoneelectrolyte is 3,000 g/mol which is greater than the initial ionexchange group equivalent weight (960 g/mol). This means that thesulfonic groups are dissociated.

[0094] (2) Preparation of an Electrolyte Membrane

[0095] We prepared an electrolyte membrane by dissolving sulfonatedpolyethersulfone electrolyte obtained by the above description (1) intoa mixture of 20 parts of N,N′-dimethylformamide, 80 parts ofcyclohexanon, and 25 parts of methylethylketone so that the solution maycontain 5% by weight of the product, spreading this solution over aglass plate by spin-coating, air-drying thereof, and vacuum-dryingthereof at 80° C. The obtained electrolyte membrane II is 45 μm thickand its ion exchange group equivalent is 0.02 S/cm.

[0096] We put said obtained electrolyte membrane II and 20 ml ofdeionized water in a Teflon-coated hermetic stainless steel container,kept the container at 120° C. for 2 weeks, cooled the container and theninspected thereof. As the result, we found the electrolyte membrane IIbroken and ragged.

[0097] (3) Preparation of a Solution for Covering Electrode Catalyst anda Membrane/Electrode Assembly

[0098] We prepared a solution II for covering electrode catalyst byadding a solvent mixture of N,N′-dimethylformamide, cyclohexanon, andmethylethylketone which contains 5% by weight of the product (see (2) tocarbon carrying 40% by weight of platinum so that the ratio by weight ofplatinum catalyst and the polymer electrolyte might be 2:1, anddispersing the mixture uniformly. Next we prepared a membrane/electrodeassembly II by coating both sides of the electrolyte membrane II(obtained by (2)) with said solution II for covering electrode catalyst,and drying thereof. The obtained membrane/electrode assembly II carries0.25 mg/cm² of platinum.

[0099] We put said obtained membrane/electrode assembly II and 20 ml ofdeionized water in a Teflon-coated hermetic stainless steel container,kept the container at 120° C. for 2 weeks, cooled the container and theninspected thereof. As the result, we found the membrane/electrodeassembly II broken and ragged.

[0100] (4) Endurance Test of Unit Cells of a Fuel Cell

[0101] We assembled the membrane/electrode assembly IV of Comparativeexample 2, thin carbon-paper packing materials (as supporting currentcollectors) at both sides of the assembly, and conductive separators(bipolar plates) provided at outer sides thereof and also working toseparate the electrodes from the chamber and to flow gases to theelectrodes into a unit cell for a solid polymer electrolyte fuel cell,and ran the unit cell for a long time at a current density of 300mA/cm². As the result, the output voltage of the unit cell was initially0.73V but exhausted after a 600-hours run, as shown by the curve 15 inFIG. 2.

[0102] The cost of the sulfopropyl polyethersulfone electrolyte is onefiftieth of the cost of perfluorosulfonic electrolyte which is preparedfrom expensive material in five processes because the sulfopropylpolyether sulfone electrolyte is prepared in a single process frompolyether sulfone which is very cheap engineering plastics on-market.

[0103] As seen from Embodiment 1 and Comparative example 1-(1), thecheap sulfopropyl polyethersulfone electrolyte unlike the cheapsulfonated aromatic hydrocarbon electrolyte (see Comparative example 1(1)) shows very good chemical stability as well as the expensiveperfluorosulfonic electrolyte, satisfying both low cost and highperformance.

[0104] Referring to Embodiment 1 and Comparative examples 1-(1) and1-(2), although the ion exchange group equivalent weight (980 g/mol) ofEmbodiment 1 (aromatic hydrocarbon electrolyte having a sulfonic groupbonded to the aromatic ring via an alkyl group) is a little greater thanthat (960 g/mol) of Comparative example 1 (aromatic hydrocarbonelectrolyte having a sulfonic group directly bonded to the aromaticring), the ion conductivity of the electrolyte membrane of Embodiment 1is greater than the ion conductivity of the electrolyte membrane ofComparative example 1. (Usually the ion conductivity of an electrolytemembrane is greater as the ion exchange group equivalent weight of theelectrolyte membrane is smaller.) Therefore the electrolyte membrane ofEmbodiment 1 is superior to that of Comparative example 1. Referring toEmbodiment 1 and Comparative examples 1-(2), the cheap sulfopropylpolyethersulfone electrolyte membrane unlike the sulfonated aromatichydrocarbon electrolyte membrane shows very good chemical stability aswell as the expensive perfluorosulfonic electrolyte membrane, satisfyingboth low cost and high performance.

[0105] Referring to Embodiment 1 and Comparative examples 1-(3), thecheap sulfopropyl polyethersulfone membrane/electrode assembly unlikethe sulfonated aromatic hydrocarbon membrane/electrode assembly showsvery good chemical stability as well as the expensive perfluorosulfonicmembrane/electrode assembly, satisfying both low cost and highperformance.

[0106] Referring to Embodiment 1 and Comparative examples 1-(4), theoutput voltage of the unit cell of a fuel cell using the electrodecatalyst covering solution of Embodiment 1 is greater than the outputvoltage of the unit cell of a fuel cell using the electrode catalystcovering solution of Comparative example 1 and the electrode catalystcovering solution of Embodiment 1 is superior to the electrode catalystcovering solution of Comparative example 1. The unit cell of a fuel cellof the present invention is low cost and as durable as the unit cell ofa perfluorosulfonic fuel cell and has substantially high chemicalstability unlike the unit cell of the sulfonated aromatic hydrocarbonfuel cell.

[0107] Referring to the curve 12 (for a unit cell of Embodiment 1) ofFIG. 2, the output voltage of the membrane/electrode assembly I isinitially 0.8 V and keeps at 0.8 V even after the unit cell runs 5,000hours, which is the same as the behavior of the output voltage of theunit cell using a perfluorosulfonic membrane/electrode assembly (bycurve 14). Contrarily, the output of curve 15 (for a unit cell ofComparative example 1) is initially 0.73 V but completely exhaustedafter the fuel cell runs 600 hours. Judging from these, it is apparentthat the unit cell of a fuel cell using an aromatic hydrocarbonelectrolyte having a sulfonic group bonded to the aromatic ring via analkyl group is more durable than the unit cell of a fuel cell using anaromatic hydrocarbon electrolyte having a sulfonic group directly bondedto the aromatic ring. Further, although both membrane/electrodeassemblies of Comparative examples 1 and 2 carry 0.25 mg/cm² ofplatinum, the output voltage of Embodiment 1 is greater than the outputvoltage of Comparative example 1. This is because the ion conductivitiesof the electrolyte and the electrode catalyst covering solution in themembrane/electrode assembly of Embodiment 1 are greater than those ofthe electrolyte and the electrode catalyst covering solution in themembrane/electrode assembly of Comparative example 1 and because themembrane/electrode assembly of Embodiment 1 is superior to themembrane/electrode assembly of Comparative example 1.

[0108] [Embodiment 2]

[0109] (1) Preparation of Sulfopropyl Polyether Etherketone

[0110] We prepared sulfopropyl polyether etherketone by setting up a500-ml 4-neck round bottom flask with a reflux condenser, a stirrer, athermometer, and a desiccant tube (containing calcium chloride in it),substituting the air inside the flask by nitrogen gas, putting 14.5 g ofpolyether etherketone, 12.2 g (0.1 mol) of propansultone and 50 ml ofdry nitrobenzene in the flask, adding 14.7 g (0.11 mol) of aluminumchloride anhydride to the mixture gradually for 30 minutes whilestirring thereof, refluxing the mixture for 30 hours after addition ofaluminum chloride anhydride is completed, dripping the reactant solutionslowly into 0.5 liter of deionized water, filtering the deionized waterto recover the precipitate (sulfopropyl polyether etherketone),repeating mixing the precipitate with deionized water andsuction-filtering the mixture until the filtrate becomes neutral, andvacuum-drying the precipitate at 120° C. for one night. The ion exchangegroup equivalent weight of the obtained sulfopropyl polyetheretherketone is 800 g/mol.

[0111] The cost of the sulfopropyl polyether etherketone electrolyte isone fortieth of the cost of perfluorosulfonic electrolyte which isprepared from expensive material in five processes because thesulfopropyl polyether etherketone electrolyte is prepared in a singleprocess from poly-ether etherketone which is very cheap engineeringplastics on-market.

[0112] We put 1.0 g of obtained sulfopropyl polyether etherketone and 20ml of deionized water in a Teflon-coated hermetic stainless steelcontainer, kept the container at 120° C. for 2 weeks, cooled thecontainer and then measured the ion exchange group equivalent weight ofsulfopropyl polyether etherketone. As the result, we found that the ionexchange group equivalent weight of sulfopropyl polyether etherketoneremains unchanged (800 g/mol) and that sulfopropyl polyether etherketoneis as stable as the expensive perfluorosulfonic electrolyte. Contrarilyas shown by the comparative example 2-(1) below, the cheap sulfonatedaromatic hydrocarbon electrolyte is deteriorated under the sametemperature and hydrolysis condition. Its ion exchange group equivalentincreases up to 2,500 g/mol (which was initially 600 g/mol) and sulfonegroups were dissociated. In other words, the low-cost sulfopropylpolyether etherketone electrolyte unlike the cheap sulfonated aromatichydrocarbon electrolyte (see Comparative example 2-(1)) shows very goodchemical stability as well as the expensive perfluorosulfonicelectrolyte, satisfying both low cost and high performance.

[0113] (2) Preparation of an Electrolyte Membrane

[0114] We prepared an electrolyte membrane III by dissolving the productobtained by the above description (1) into a solvent solution ofN-methyl pyrolidone, spreading this solution over a glass plate byspin-coating, air-drying thereof, and vacuum-drying thereof at 80° C.The obtained electrolyte membrane III is 42 μm thick.

[0115] We put said obtained electrolyte membrane III and 20 ml ofdeionized water in a Teflon-coated hermetic stainless steel container,kept the container at 120° C. for 2 weeks, cooled the container and thenmeasured its ion exchange group equivalent weight. As the result, wefound that the ion exchange group equivalent weight of the obtainedelectrolyte membrane remains unchanged as well as the expensiveperfluorosulfonic electrolyte. The membrane itself is tough enough.Contrarily as shown by the comparative example 2-(2), the comparativelycheap sulfonated aromatic hydrocarbon electrolyte IV is broken andragged under the same temperature and hydrolysis condition. In otherwords, the low-cost sulfopropyl polyethersulfone electrolyte unlike thecheap sulfonated aromatic hydrocarbon electrolyte IV (see Comparativeexample 2-(2)) shows very good chemical stability as well as theexpensive perfluorosulfonic electrolyte, satisfying both low cost andhigh performance.

[0116] (3) Preparation of a Solution for Covering Electrode Catalyst anda Membrane/Electrode Assembly

[0117] We prepared a solution III for covering electrode catalyst byadding a N-methylpyrolidone solution to carbon carrying 40% by weight ofplatinum so that the ratio by weight of platinum catalyst and thepolymer electrolyte might be 2:1, and dispersing the mixture uniformly.Next we prepared a membrane/electrode assembly III by coating both sidesof the electrolyte membrane III (obtained by (2)) with said solution IIIfor covering electrode catalyst, and drying thereof. The obtainedmembrane/electrode assembly III carries 0.25 mg/cm² of platinum.Similarly we prepared a membrane/electrode assembly III′ carrying 0.25mg/cm² of platinum by coating both sides of the electrolyte membrane III(obtained by (2)) with said solution IV for covering electrode catalyststated by Comparative example 2-(3), and drying thereof.

[0118] We prepared a paste (a solution for covering electrode catalyst)by adding an alcohol-water mixture of 5% by weight as perfluoro sulfonicelectrolyte to carbon carrying 40% by weight of platinum so that theratio by weight of platinum catalyst and the polymer electrolyte mightbe 2:1, and dispersing the mixture uniformly. Next we coated both sidesof the electrolyte membrane III (obtained by (2)) with this paste(solution). However, the paste could not be uniformly spread over theelectrolyte membrane and we could not get a membrane/electrode assembly.

[0119] We put said obtained membrane/electrode assembly III and 20 ml ofdeionized water in a Teflon-coated hermetic stainless steel containerand kept the container at 120° C. for 2 weeks. As the result, we foundthat the obtained electrolyte/membrane assembly III remains unchanged aswell as the membrane/electrode assembly prepared from the expensiveperfluorosulfonic membrane and the perfluorosulfonic electrolyte. Themembrane itself is tough enough.

[0120] Similarly, we put said obtained membrane/electrode assembly III′and 20 ml of deionized water in a Teflon-coated hermetic stainless steelcontainer and kept the container at 120° C. for 2 weeks. As the result,we found that the membrane/electrode assembly III′ has enough powergenerating performance although the electrode was partially separated.

[0121] Contrarily as shown by the comparative example 2-(3), themembrane/electrode assembly III prepared by comparatively cheapsulfonated aromatic hydrocarbon electrolyte IV and the electrodecatalyst covering solution IV is broken and ragged under the sametemperature and hydrolysis condition. In other words, the low-costsulfopropyl polychlorotrifluoroethylene membrane/electrode assemblyunlike the cheap sulfonated aromatic hydrocarbon membrane/electrodeassembly (see Comparative example 2-(3) is as stable as the expensiveperfluorosulfonic membrane/electrolyte assembly, and satisfies both lowcost and high performance.

[0122] (4) Evaluation of Output of the Unit Cells of a Fuel Cell

[0123] We evaluated the output performance of a fuel cell by dippingsaid membrane/electrode assemblies III and III′ in deionized boilingwater to let the assemblies absorb water and setting each wetmembrane/electrode assembly in a sample unit. FIG. 4 shows arelationship between current density and voltage of a unit cell of afuel cell containing membrane/electrode assembly III. The output voltageof the fuel cell is 0.6 V at a current density of 1 A/cm² and 0.76 V ata current density or 300 mA/cm². This fuel cell is fully available as asolid polymer electrolyte fuel cell.

[0124] We prepared unit cells for solid polymer electrolyte fuel cellsby respectively assembling the membrane/electrode assembies III and III′of Comparative example 2, thin carbon-paper packing materials (assupporting current collectors) at both sides of the assembly, andconductive separators (bipolar plates) provided at outer sides thereofand also working to separate the electrodes from the chamber and to flowgases to the electrodes into a unit cell for a solid polymer electrolytefuel cell, and ran each unit cell for a long time at a current densityof 300 mA/cm². FIG. 5 shows the relationship between the output voltageand the running time of the unit cell. The curve 16 in FIG. 5 is theresult of the endurance test of the unit cell using themembrane/electrode assembly III in accordance with the presentinvention. The curve 17 in FIG. 5 is the result of the endurance test ofthe unit cell using the membrane/electrode assembly III′. The curve 18in FIG. 5 is the result of the endurance test of the unit cell using aperfluorosulfonic membrane/electrode assembly. As shown by curve 16 inFIG. 5, the output voltage of the unit cell is initially 0.76 V andkeeps at 0.76 V even after the unit cell runs 5,000 hours, which is thesame as the behavior of the output voltage of the unit cell using aperfluorosulfonic membrane (by curve 18). As shown by curve 19 in FIG.5, the output voltage (of a unit cell using sulfonated aromatichydrocarbon electrolyte of Comparative example 2 below) is initially0.73 V but completely exhausted after the fuel cell runs 5000 hours.

[0125] Judging from these, it is apparent that the unit cell of a fuelcell using an aromatic hydrocarbon electrolyte having a sulfonic groupbonded to the aromatic ring via an alkyl group is more durable than theunit cell of a fuel cell using an aromatic hydrocarbon electrolytehaving a sulfonic group directly bonded to the aromatic ring. Further,although both membrane/electrode assemblies of Embodiment 2 andComparative example 2 carry 0.25 mg/cm² of platinum, the output voltageof Embodiment 2 is greater than the output voltage of Comparativeexample 2.

[0126] This is because the ion conductivities of the electrolyte and theelectrode catalyst covering solution in the membrane/electrode assemblyof Embodiment 2 are greater than those of the electrolyte and theelectrode catalyst covering solution in the membrane/electrode assemblyof Comparative example 2 and because the membrane/electrode assembly ofEmbodiment 2 is superior to the membrane/electrode assembly ofComparative example 2.

[0127] (5) Preparation of Fuel Cells

[0128] We piled up 36 unit cells which were prepared in (4) to form asolid polymer electrolyte fuel cell. This fuel cell outputs 3 KW.

COMPARATIVE EXAMPLE 2

[0129] (1) Preparation of Sulfonated Polyether Etherketone Sulfone

[0130] We prepared sulfonated polyether etherketone electrolyte bysetting up a 500-ml 4-neck round bottom flask with a reflux condenser, astirrer, a thermometer, and a desiccant tube (containing calciumchloride in it), substituting the air inside the flask by nitrogen gas,putting 6.7 g of polyether etherketone (PEEK) and 100 ml of 96%concentrated sulfuric acid in the flask, stirring the mixture at 60° C.for 60 minutes in the presence of nitrogen gas, adding oleum (containing20% by weight SO₃) to the solution while stirring the solution in theflow of nitrogen gas to make 98.5% by weight sulfuric acid, heating thesolution at 80° C. for 30 minutes, dripping the reactant solution slowlyinto 15 liters of deionized water, filtering the deionized water torecover the precipitate (sulfonated polyether etherketone), repeatingmixing the precipitate with deionized water and suction-filtering themixture until the filtrate becomes neutral, and vacuum-drying theprecipitate at 80° C. for one night. The ion exchange group equivalentweight of the obtained sulfonated polyether etherketone electrolyte is600 g/mol.

[0131] We put 1.0 g of obtained sulfonated polyether etherketoneelectrolyte and 20 ml of deionized water in a Teflon-coated hermeticstainless steel container, kept the container at 120° C. for 2 weeks,cooled the container and then measured the ion exchange group equivalentweight of sulfonated polyether etherketone. As the result, we found thatthe ion exchange group equivalent weight of sulfonated polyetheretherketone electrolyte is 2,500 g/mol which is greater than the initialion exchange group equivalent weight (960 g/mol). This means that thesulfonic groups are dissociated.

[0132] (2) Preparation of an Electrolyte Membrane

[0133] We prepared an electrolyte membrane by dissolving sulfonatedpolyether etherketone electrolyte obtained by the above description (1)into a mixture of 20 parts of N,N′-dimethylformamide, 80 parts ofcyclohexanon, and 25 parts of methylethylketone so that the solution maycontain 5% by weight of the product, spreading this solution over aglass plate by spin-coating, air-drying thereof, and vacuum-dryingthereof at 80° C. The obtained electrolyte membrane IV is 45 μm thickand its ion exchange group equivalent is 0.02 S/cm.

[0134] We put said obtained electrolyte membrane IV and 20 ml ofdeionized water in a Teflon-coated hermetic stainless steel container,kept the container at 120° C. for 2 weeks, cooled the container and theninspected thereof. As the result, we found the electrolyte membrane IVbroken and ragged.

[0135] (3) Preparation of a Solution for Covering Electrode Catalyst anda Membrane/Electrode Assembly

[0136] We prepared a paste (a solution IV for covering electrodecatalyst) by adding a solvent mixture of N,N′-dimethylformamide,cyclohexanon, and methylethylketone which contains 5% by weight of theproduct (see (2)) to carbon carrying 40% by weight of platinum so thatthe ratio by weight of platinum catalyst and the polymer electrolytemight be 2:1, and dispersing the mixture uniformly. Next we prepared amembrane/electrode assembly IV by coating both sides of the electrolytemembrane IV (obtained by (2)) with said solution IV for coveringelectrode catalyst, and drying thereof. The obtained membrane/electrodeassembly IV carries 0.25 mg/cm² of platinum.

[0137] We put said obtained membrane/electrode assembly IV and 20 ml ofdeionized water in a Teflon-coated hermetic stainless steel container,kept the container at 120° C. for 2 weeks, cooled the container and theninspected thereof. As the result, we found the membrane/electrodeassembly IV broken and ragged.

[0138] (4) Endurance Test of Unit Cells of a Fuel Cell

[0139] We prepared a unit cell for a solid polymer electrolyte fuel cellby assembling the membrane/electrode assembly IV of Comparative example2, thin carbon-paper packing materials (as supporting currentcollectors) in close contact at both sides of the assembly, andconductive separators (bipolar plates) provided at outer sides thereofand also working to separate the electrodes from the chamber and to flowgases to the electrodes and ran the unit cell for a long time at acurrent density of 300 mA/cm². As the result, the output voltage of theunit cell was initially 0.73V but exhausted after a 5,000-hours run, asshown by the curve 19 in FIG. 5.

[0140] The cost of the sulfopropyl polyether etherketone electrolyte isone fortieth of the cost of perfluorosulfonic electrolyte which isprepared from expensive material in five processes because thesulfopropyl polyether etherketone electrolyte is prepared in a singleprocess from polyether etherketone which is very cheap engineeringplastics on-market.

[0141] As seen from Embodiment 2 and Comparative example 2-(1), thearomatic hydrocarbon electrolyte (Embodiment 2) having a sulfonic groupbonded to the aromatic ring via an alkyl group is more resistant to thehot deionized water (120° C.) than the aromatic hydrocarbon electrolyte(Comparative example 2) having a sulfonic group directly bonded to thearomatic ring.

[0142] Referring to Embodiment 1 and Comparative examples 2-(3), theelectrode catalyst covering solution of Embodiment 2 is more suitablefor the aromatic hydrocarbon membrane than the perfluorosulfonicelectrode catalyst covering solution. Referring to Embodiment 2 andComparative examples 2-(4), the output voltage of a unit cell using theelectrode catalyst covering solution of Embodiment 2 is greater than theoutput voltage of a unit cell using the electrode catalyst coveringsolution of Comparrative example 2. Therefore, the electrode catalystcovering solution of Embodiment 2 is superior to the electrode catalystcovering solution of Comparrative example 2.

[0143] Referring to the curve 16 of FIG. 5, the output voltage of theunit cell of Embodiment 2 is initially 0.8 V and keeps at 0.8 V evenafter the unit cell runs 5,000 hours, which is the same as the behaviorof the output voltage of the unit cell using a perfluorosulfonicmembrane/electrode assembly (by curve 18). Contrarily, the output ofcurve 19 (for a unit cell of Comparative example 2) is initially 0.73 Vand completely exhausted after the fuel cell runs 5000 hours. Judgingfrom these, it is apparent that the unit cell of a fuel cell using anaromatic hydrocarbon electrolyte having a sulfonic group bonded to thearomatic ring via an alkyl group is more durable than the unit cell of afuel cell using an aromatic hydrocarbon electrolyte having a sulfonicgroup directly bonded to the aromatic ring. Further, although bothmembrane/electrode assemblies of Embodiment 2 and Comparative examples 2carry 0.25 mg/cm² of platinum, the output voltage of Embodiment 2 isgreater than the output voltage of Comparative example 2. This isbecause the ion conductivities of the electrolyte and the electrodecatalyst covering solution in the membrane/electrode assembly ofEmbodiment 2 are greater than those of the electrolyte and the electrodecatalyst covering solution in the membrane/electrode assembly ofComparative example 2 and because the membrane/electrode assembly ofEmbodiment 2 is superior to the membrane/electrode assembly ofComparative example 2.

[0144] [Embodiment 3]

[0145] (1) Preparation of Sulfopropyl Poly-phenylene Sulfide

[0146] We prepared sulfopropyl polyether etherketone by setting up a500-ml 4-neck round bottom flask with a reflux condenser, a stirrer, athermometer, and a desiccant tube (containing calcium chloride in it),substituting the air inside the flask by nitrogen gas, putting 10.8 g ofpoly-phenylene sulfide (PPS), 12.2 g (0.1 mol) of propansultone and 50ml of dry nitrobenzene in the flask, adding 14.7 g (0.11 mol) ofaluminum chloride anhydride to the mixture gradually for 30 minuteswhile stirring thereof, refluxing the mixture for 10 hours afteraddition of aluminum chloride anhydride is completed, dripping thereactant solution slowly into 0.5 liter of deionized water, filteringthe deionized water to recover the precipitate (sulfopropylpoly-phenylene sulfide), repeating mixing the precipitate with deionizedwater and suction-filtering the mixture until the filtrate becomesneutral, and vacuum-drying the precipitate at 120° C. for one night. Theion exchange group equivalent weight of the obtained sulfopropylpoly-phenylene sulfide is 520 g/mol.

[0147] The cost of the sulfopropyl poly-phenylene sulfide electrolyte isone fiftieth of the cost of perfluorosulfonic electrolyte which isprepared from expensive material in five processes because thesulfopropyl poly-phenylene sulfide electrolyte is prepared in a singleprocess from poly-phenylene sulfide which is very cheap engineeringplastics on-market.

[0148] We put 1.0 g of obtained sulfopropyl poly-phenylene sulfide and20 ml of deionized water in a Teflon-coated hermetic stainless steelcontainer, kept the container at 120° C. for 2 weeks, cooled thecontainer and then measured the ion exchange group equivalent weight ofsulfopropyl poly-phenylene sulfide. As the result, we found that the ionexchange group equivalent weight of sulfopropyl poly-phenylene sulfideremains unchanged (520 g/mol) and that sulfopropyl poly-phenylenesulfide is as stable as the expensive perfluorosulfonic electrolyte.Contrarily as shown by the comparative example 3-(1) below, the cheapsulfonated aromatic hydrocarbon electrolyte is deteriorated under thesame temperature and hydrolysis condition. Its ion exchange groupequivalent increases up to 3,500 g/mol (which was initially 500 g/mol)and sulfon groups were dissociated. In other words, the low-costsulfopropyl poly-phenylene sulfide electrolyte unlike the cheapsulfonated aromatic hydrocarbon electrolyte (see Comparative example3-(1)) shows very good chemical stability as well as the expensiveperfluorosulfonic electrolyte, satisfying both low cost and highperformance.

[0149] (2) Preparation of an Electrolyte Membrane

[0150] We prepared an electrolyte membrane V by dissolving the product(sulfopropyl poly-phenylene sulfide) obtained by the above description(1) into a solvent solution of N-methyl pyrolidone, spreading thissolution over a glass plate by spin-coating, air-drying thereof, andvacuum-drying thereof at 80° C. The obtained electrolyte membrane V is46 μm thick.

[0151] We put said obtained electrolyte membrane V and 20 ml ofdeionized water in a Teflon-coated hermetic stainless steel container,kept the container at 120° C. for 2 weeks, cooled the container and thenmeasured its ion exchange group equivalent weight. As the result, wefound that the ion exchange group equivalent weight of the obtainedelectrolyte membrane remains unchanged as well as the expensiveperfluorosulfonic electrolyte. The membrane itself is tough enough.Contrarily as shown by the comparative example 3-(2), the comparativelycheap sulfonated aromatic hydrocarbon electrolyte VI is broken andragged under the same temperature and hydrolysis condition. In otherwords, the low-cost sulfopropyl poly-phenylene sulfide electrolyteunlike the cheap sulfonated aromatic hydrocarbon electrolyte IV (seeComparative example 3-(2)) shows very good chemical stability as well asthe expensive perfluorosulfonic electrolyte, satisfying both low costand high performance.

[0152] (3) Preparation of a Solution for Covering Electrode Catalyst anda Membrane/Electrode Assembly

[0153] We prepared a solution V for covering electrode catalyst byadding a N-methylpyrolidone solution to carbon carrying 40% by weight ofplatinum so that the ratio by weight of platinum catalyst and thepolymer electrolyte might be 2:1, and dispersing the mixture uniformly.Next we coated one side of the electrolyte membrane V (obtained by (2))with said electrode catalyst covering solution V, and drying thereof.Further, we prepared a solution V′ for covering electrode catalyst byadding a N-methylpyrolidone solution to carbon carrying 40% by weight ofplatinum-ruthenium alloy so that the ratio by weight ofplatinum-ruthenium alloy catalyst and the polymer electrolyte might be2:1, and dispersing the mixture uniformly. Next we covered the otherside of the membrane V (obtained by (2)) with said electrode catalystcovering solution V′, and drying thereof. Thus we prepared amembrane/electrode assembly V having one side (oxygen electrode) of 0.25mg/cm² of platinum and the other side (hydrogen electrode) of 0.3 mg/cm²of platinum-ruthenium alloy.

[0154] In the same manner but using the electrode catalyst coveringsolution VI of Comparative example 3, we prepared a membrane/electrodeassembly V′ having one side (oxygen electrode) of 0.25 mg/cm² ofplatinum and the other side (hydrogen electrode) of 0.3 mg/cm² ofplatinum-ruthenium alloy.

[0155] We prepared a paste (a solution for covering electrode catalyst)by adding an alcohol-water mixture of 5% by weight as perfluoro sulfonicelectrolyte to carbon carrying 40% by weight of platinum so that theratio by weight of platinum catalyst and the polymer electrolyte mightbe 2:1, and dispersing the mixture uniformly. Next we coated both sidesof the electrolyte membrane V (obtained by (2)) with this paste(solution). However, the paste could not be uniformly spread over theelectrolyte membrane and we could not get a membrane/electrode assembly.

[0156] We put said obtained membrane/electrode assembly V and 20 ml ofdeionized water in a Teflon-coated hermetic stainless steel containerand kept the container at 120° C. for 2 weeks. As the result, we foundthat the obtained electrolyte/membrane assembly V remains unchanged aswell as the membrane/electrode assembly prepared from the expensiveperfluorosulfonic membrane and the perfluorosulfonic electrolyte. Themembrane itself is tough enough.

[0157] Similarly, we put said obtained membrane/electrode assembly V′and 20 ml of deionized water in a Teflon-coated hermetic stainless steelcontainer and kept the container at 120° C. for 2 weeks. As the result,we found that the membrane/electrode assembly V′ has enough powergenerating performance although the electrode was partially separated.

[0158] Contrarily as shown by the comparative example 1-(3), themembrane/electrode assembly VI prepared by comparatively cheapsulfonated aromatic hydrocarbon electrolyte VI and the electrodecatalyst covering solution VI is broken and ragged under the sametemperature and hydrolysis condition. In other words, the low-costsulfopropyl polyphenylene sulfide membrane/electrode assembly unlike thecheap sulfonated aromatic hydrocarbon membrane/electrode assembly (seeComparative example 3-(3) is as stable as the expensiveperfluorosulfonic membrane/electrolyte assembly, and satisfies both lowcost and high performance.

[0159] (4) Evaluation of Output of the Unit Cells of a Fuel Cell

[0160] We evaluated the output performance of a fuel cell by dippingsaid membrane/electrode assembly in deionized boiling water to let theassembly absorb water and setting the wet membrane/electrode assembly ina sample unit. FIG. 6 shows a relationship between current density andvoltage of a unit cell of a fuel cell containing membrane/electrodeassembly VI. The output voltage of the fuel cell is 0.63 V at a currentdensity of 1 A/cm² and 0.78 V at a current density or 300 mA/cm². Thisfuel cell is fully available as a solid polymer electrolyte fuel cell.

[0161] We ran the unit cell of said solid polymer electrolyte fuel cellfor a long time at a current density of 300 mA/cm². FIG. 7 shows therelationship between the output voltage and the running time of the unitcell. The curve 20 in FIG. 7 is the result of the endurance test of theunit cell using the membrane/electrode assembly V in accordance with thepresent invention. The curve 21 in FIG. 7 is the result of the endurancetest of the unit cell using the membrane/electrode assembly V′. Thecurve 22 in FIG. 7 is the result of the endurance test of the unit cellusing a perfluorosulfonic membrane/electrode assembly. As shown by curve20 in FIG. 7, the output voltage of the unit cell is initially 0.78 Vand keeps at 0.78 V even after the unit cell runs 5,000 hours, which isthe same as the behavior of the output voltage of the unit cell using aperfluorosulfonic membrane (by curve 22). As shown by curve 23 in FIG.7, the output voltage (of a unit cell using sulfonated aromatichydrocarbon electrolyte of Comparative example 3 below) is initially0.63 V but completely exhausted after the fuel cell runs 600 hours.Judging from these, it is apparent that the unit cell of a fuel cellusing an aromatic hydrocarbon electrolyte having a sulfonic group bondedto the aromatic ring via an alkyl group is more durable than the unitcell of a fuel cell using an aromatic hydrocarbon electrolyte having asulfonic group directly bonded to the aromatic ring.

[0162] Further, although both membrane/electrode assemblies ofEmbodiment 3 and Comparative example 3 carry 0.25 mg/cm² of platinum,the output voltage of Embodiment 3 is greater than the output voltage ofComparative example 3. This is because the ion conductivities of theelectrolyte and the electrode catalyst covering solution in themembrane/electrode assembly of Embodiment 3 are greater than those ofthe electrolyte and the electrode catalyst covering solution in themembrane/electrode assembly of Comparative example 3 and because themembrane/electrode assembly of Embodiment 3 is superior to themembrane/electrode assembly of Comparative example 3.

[0163] (5) Preparation of Fuel Cells

[0164] We piled up 36 unit cells which were prepared in (4) to form asolid polymer electrolyte fuel cell. This fuel cell outputs 3 KW.

COMPARATIVE EXAMPLE 3

[0165] (1) Preparation of Sulfonated Poly-phenylene Sulfide

[0166] We prepared sulfopropyl polyether etherketone by setting up a500-ml 4-neck round bottom flask with a reflux condenser, a stirrer, athermometer, and a desiccant tube (containing calcium chloride in it),substituting the air inside the flask by nitrogen gas, putting 12 g ofpoly-phenylene sulfide (PPS) and 220 ml of chlorosulfuric acid, stirringthe mixture for 30 minutes at 5° C. in the flow of a nitrogen gas todissolve PPS, keeping still at 20° C. for 150 minutes and at 50° C. for60 minutes, dripping the reactant solution slowly into 15 liters ofdeionized water, filtering the deionized water to recover theprecipitate (sulfonated poly-phenylene sulfide), repeating mixing theprecipitate with deionized water and suction-filtering the mixture untilthe filtrate becomes neutral, and vacuum-drying the precipitate at 80°C. for one night. The ion exchange group equivalent weight of theobtained sulfonated poly-phenylene sulfide is 500 g/mol.

[0167] We put 1.0 g of obtained sulfonated polyether sulfone and 20 mlof deionized water in a Teflon-coated hermetic stainless steelcontainer, kept the container at 120° C. for 2 weeks, cooled thecontainer and then measured the ion exchange group equivalent weight ofsulfonated poly-phenylene sulfide. As the result, we found that the ionexchange group equivalent weight of sulfonated poly-phenylene sulfide is3,500 g/mol which is greater than the initial ion exchange groupequivalent weight. This means that the sulfonic groups are dissociated.

[0168] (2) Preparation of an Electrolyte Membrane

[0169] We prepared a sulfonated poly-phenylene sulfide electrolytemembrane by dissolving sulfonated poly-phenylene sulfide electrolyteobtained by the above description (1) into a mixture of 20 parts ofN,N′-dimethylformamide, 80 parts of cyclohexanon, and 25 parts ofmethylethylketone, spreading this solution over a glass plate byspin-coating, air-drying thereof, and vacuum-drying thereof at 80° C.The obtained sulfonated poly-phenylene sulfide electrolyte membrane VIis 45 μm thick and its ion exchange group equivalent is 0.02 S/cm.

[0170] We put said sulfonated poly-phenylene sulfide electrolytemembrane VI and 20 ml of deionized water in a Teflon-coated hermeticstainless steel container and kept the container at 120° C. for 2 weeks.As the result, we found the sulfonated poly-phenylene sulfideelectrolyte membrane VI broken and ragged.

[0171] (3) Preparation of a Solution for Covering Electrode Catalyst anda Membrane/Electrode Assembly

[0172] We prepared a paste (a solution VI for covering electrodecatalyst) by adding a solvent mixture of N,N′-dimethylformamide,cyclohexanon, and methylethylketone which contains 5% by weight of theproduct (see (2)) to carbon carrying 40% by weight of platinum so thatthe ratio by weight of platinum catalyst and the polymer electrolytemight be 2 : 1, and dispersing the mixture uniformly. Next we prepared amembrane/electrode assembly VI by coating both sides of the electrolytemembrane VI (obtained by (2)) with said solution VI for coveringelectrode catalyst, and drying thereof. The obtained membrane/electrodeassembly IV carries 0.25 mg/cm² of platinum.

[0173] We put said obtained membrane/electrode assembly VI and 20 ml ofdeionized water in a Teflon-coated hermetic stainless steel container,kept the container at 120° C. for 2 weeks, cooled the container and theninspected thereof. As the result, we found the membrane/electrodeassembly VI broken and ragged.

[0174] (4) Endurance Test of Unit Cells of a Fuel Cell

[0175] We prepared a unit cell for a solid polymer electrolyte fuel cellby assembling the membrane/electrode assembly VI of Comparative example3, thin carbon-paper packing materials (as supporting currentcollectors) in close contact at both sides of the assembly, andconductive separators (bipolar plates) provided at outer sides thereofand also working to separate the electrodes from the chamber and to flowgases to the electrodes and ran the unit cell for a long time at acurrent density of 300 mA/cm². As the result, the output voltage of theunit cell was initially 0.63V but exhausted after a 600-hours run, asshown by the curve 23 in FIG. 7.

[0176] The cost of the sulfonated poly-phenylene sulfide electrolyte isone fiftieth of the cost of perfluorosulfonic electrolyte which isprepared from expensive material in five processes because thesulfonated poly-phenylene sulfide electrolyte is prepared in a singleprocess from poly-phenylene sulfide which is very cheap engineeringplastics on-market.

[0177] As seen from Embodiment 3 and Comparative example 3-(1), thearomatic hydrocarbon electrolyte (Embodiment 3) having a sulfonic groupbonded to the aromatic ring via an alkyl group is more resistant to thehot deionized water (120° C.) than the aromatic hydrocarbon electrolyte(Comparative example 3) having a sulfonic group directly bonded to thearomatic ring.

[0178] Referring to Embodiment 3 and Comparative examples 3-(1) and3-(2), although the ion exchange group equivalent weight (520 g/mol) ofEmbodiment 3 (aromatic hydrocarbon electrolyte having a sulfonic groupbonded to the aromatic ring via an alkyl group) is a little greater thanthat (500 g/mol) of Comparative example 3 (aromatic hydrocarbonelectrolyte having a sulfonic group directly bonded to the aromaticring), the ion conductivity of the electrolyte membrane of Embodiment 3is greater than the ion conductivity of the electrolyte membrane ofComparative example 3. (Usually the ion conductivity of an electrolytemembrane is greater as the ion exchange group equivalent weight of theelectrolyte membrane is smaller.) Therefore the electrolyte membrane ofEmbodiment 3 is superior to that of Comparative example 3.

[0179] Referring to Embodiment 3 and Comparative examples 3-(3), theelectrode catalyst covering solution of Embodiment 3 is more suitablefor the aromatic hydrocarbon membrane than the perfluorosulfonicelectrode catalyst covering solution. Referring to Embodiment 3 andComparative examples 3-(4), the output voltage of a unit cell using theelectrode catalyst covering solution of Embodiment 3 is greater than theoutput voltage of a unit cell using the electrode catalyst coveringsolution of Comparrative example 3. Therefore, the electrode catalystcovering solution of Embodiment 3 is superior to the electrode catalystcovering solution of Comparrative example 3.

[0180] Referring to the curve 20 of FIG. 7, the output voltage of theunit cell of Embodiment 3 is initially 0.78 V and keeps at 0.78 V evenafter the unit cell runs 5,000 hours, which is the same as the behaviorof the output voltage of the unit cell using a perfluorosulfonicmembrane/electrode assembly (by curve 22). Contrarily, the output ofcurve 23 (for a unit cell of Comparative example 3) is initially 0.63 Vand completely exhausted after the fuel cell runs 600 hours. Judgingfrom these, it is apparent that the unit cell of a fuel cell using anaromatic hydrocarbon electrolyte having a sulfonic group bonded to thearomatic ring via an alkyl group is more durable than the unit cell of afuel cell using an aromatic hydrocarbon electrolyte having a sulfonicgroup directly bonded to the aromatic ring. Further, although bothmembrane/electrode assemblies of Embodiment 3 and Comparative examples 3carry 0.25 mg/cm² of platinum, the output voltage of Embodiment 3 isgreater than the output voltage of Comparative example 3. This isbecause the ion conductivities of the electrolyte and the electrodecatalyst covering solution in the membrane/electrode assembly ofEmbodiment 3 are greater than those of the electrolyte and the electrodecatalyst covering solution in the membrane/electrode assembly ofComparative example 3 and because the membrane/electrode assembly ofEmbodiment 3 is superior to the membrane/electrode assembly ofComparative example 3.

[0181] [Embodiment 4]

[0182] (1) Preparation of Sulfopropyl Reformed Polyphenylene Oxide

[0183] We prepared sulfopropyl reformed polyphenylene oxide by settingup a 500-ml 4-neck round bottom flask with a reflux condenser, astirrer, a thermometer, and a desiccant tube (containing calciumchloride in it), substituting the air inside the flask by nitrogen gas,putting 12.0 g of polyphenylene oxide (m-PPE), 12.2 g (0.1 mol) ofpropansultone and 50 ml of dimethyl sulfoxide, adding 14.7 g (0.11 mol)of aluminum chloride anhydride to the mixture gradually for 30 minuteswhile stirring thereof, keeping the mixture at 150° C. for 8 hours,dripping the reactant solution into 500 ml of iced water containing 25ml of concentrated hydrochloric acid to stop the reaction, separatingthe organic precipitate, washing thereof, neutralizing thereof with anaqueous solution of sodium carbonate containing a few drops of octylalcohol, separating aluminum hydroxide by filtration, decoloring thefiltrate by active carbon, and evaporating the solvent. The ion exchangegroup equivalent weight of the obtained sulfopropyl reformedpolyphenylene oxide is 370 g/mol.

[0184] The cost of the sulfopropyl polyphenylene oxide electrolyte isone fiftieth of the cost of perfluorosulfonic electrolyte which isprepared from expensive material in five processes because thesulfopropyl polyphenylene oxide electrolyte is prepared in a singleprocess from polyphenylene oxide which is very cheap engineeringplastics on-market.

[0185] We put 1.0 g of said sulfopropyl reformed polyphenylene oxide and20 ml of deionized water in a Teflon-coated hermetic stainless steelcontainer, kept the container at 120° C. for 2 weeks, cooled thecontainer and then measured the ion exchange group equivalent weight ofthe sulfopropyl reformed polyphenylene oxide electrolyte. As the result,we found that the ion exchange group equivalent weight of sulfopropylreformed polyphenylene oxide remains unchanged (520 g/mol) and thatsulfopropyl reformed polyphenylene oxide is as stable as the expensiveperfluorosulfonic electrolyte. Contrarily as shown by the comparativeexample 4-(1) below, the cheap sulfonated aromatic hydrocarbonelectrolyte is deteriorated under the same temperature and hydrolysiscondition. Its ion exchange group equivalent increases up to 3,500 g/mol(which was initially 490 g/mol) and sulfone groups were dissociated.

[0186] In other words, the low-cost sulfopropyl reformed polyphenyleneoxide electrolyte unlike the cheap sulfonated aromatic hydrocarbonelectrolyte (see Comparative example 4-(1)) shows very good chemicalstability as well as the expensive perfluorosulfonic electrolyte,satisfying both low cost and high performance.

[0187] (2) Preparation of an Electrolyte Membrane

[0188] We prepared a sulfopropyl reformed polyphenylene oxideelectrolyte membrane by dissolving sulfopropyl reformed polyphenyleneoxide electrolyte obtained by the above description (1) into a mixtureof 20 parts of N,N′-dimethylformamide, 80 parts of cyclohexanon, and 25parts of methylethylketone so that the solution may contain 5% by weightof the product, spreading this solution over a glass plate byspin-coating, air-drying thereof, and vacuum-drying thereof at 80° C.The obtained sulfopropyl reformed polyphenylene oxide electrolytemembrane VII is 42 μm thick and its ion exchange group equivalent is0.01 S/cm.

[0189] We put said obtained electrolyte membrane VII and 20 ml ofdeionized water in a Teflon-coated hermetic stainless steel containerand kept the container at 120° C. for 2 weeks. As the result, we foundthat the ion exchange group equivalent weight of the obtainedelectrolyte membrane remains unchanged as well as the expensiveperfluorosulfonic electrolyte. The membrane itself is tough enough.Contrarily as shown by the comparative example 4-(2), the comparativelycheap sulfonated aromatic hydrocarbon electrolyte VIII is broken andragged under the same temperature and hydrolysis condition. In otherwords, the low-cost sulfopropyl reformed polyphenylene oxide electrolyteunlike the cheap sulfonated aromatic hydrocarbon electrolyte (seeComparative example 4-(2)) shows very good chemical stability as well asthe expensive perfluorosulfonic electrolyte, satisfying both low costand high performance.

[0190] (3) Preparation of a Solution for Covering Electrode Catalyst anda Membrane/Electrode Assembly

[0191] We prepared a paste (a solution VII for covering electrodecatalyst) by adding a solvent mixture of N,N′-dimethylformamide,cyclohexanon, and methylethylketone which contains 5% by weight of theproduct (see (2)) to carbon carrying 40% by weight of platinum so thatthe ratio by weight of platinum catalyst and the polymer electrolytemight be 2:1, and dispersing the mixture uniformly. Next we prepared amembrane/electrode assembly IV by coating both sides of the electrolytemembrane VII (obtained by (2)) with said solution VII for coveringelectrode catalyst, and drying thereof. The obtained membrane/electrodeassembly VII carries 0.25 mg/cm² of platinum.

[0192] We put said obtained membrane/electrode assembly VII and 20 ml ofdeionized water in a Teflon-coated hermetic stainless steel containerand kept the container at 120° C. for 2 weeks. As the result, we foundthat the obtained electrolyte/membrane assembly VII remains unchanged aswell as the membrane/electrode assembly prepared from the expensiveperfluorosulfonic membrane and the perfluorosulfonic electrolyte. Themembrane itself is tough enough.

[0193] Contrarily as shown by the comparative example 4-(3), themembrane/electrode assembly VIII prepared by comparatively cheapsulfonated aromatic hydrocarbon electrolyte VIII and the electrodecatalyst covering solution VIII is broken and ragged under the sametemperature and hydrolysis condition. In other words, the low-costsulfopropyl reformed polyphenylene oxide membrane/electrode assemblyunlike the cheap sulfonated aromatic hydrocarbon membrane/electrodeassembly (see Comparative example 4-(3) is as stable as the expensiveperfluorosulfonic membrane/electrolyte assembly, and satisfies both lowcost and high performance.

[0194] (4) Evaluation of Output of the Unit Cells of a Fuel Cell

[0195] We evaluated the output performance of a fuel cell by dippingsaid membrane/electrode assembly VII in deionized boiling water to letthe assembly absorb water and setting the wet membrane/electrodeassembly in a sample unit. FIG. 8 shows a relationship between currentdensity and voltage of a unit cell of a fuel cell containingmembrane/electrode assembly VII. The output voltage of the fuel cell is0.69 V at a current density of 1 A/cm² and 0.82 V at a current densityor 300 mA/cm². This fuel cell is fully available as a solid polymerelectrolyte fuel cell. We ran said unit cell for a long time at acurrent density of 300 mA/cm². FIG. 9 shows the relationship between theoutput voltage and the running time of the unit cell. The curve 24 inFIG. 9 is the result of the endurance test of the unit cell using themembrane/electrode assembly VII in accordance with the presentinvention.

[0196] The curve 25 in FIG. 9 is the result of the endurance test of theunit cell using a perfluorosulfonic membrane/electrode assembly. Asshown by curve 24 in FIG. 9, the output voltage of the unit cell isinitially 0.82 V and keeps at the voltage level even after the unit cellruns 5,000 hours, which is the same as the behavior of the outputvoltage of the unit cell using a perfluorosulfonic membrane (by curve25). As shown by curve 26 in FIG. 9, the output voltage (of a unit cellusing sulfonated aromatic hydrocarbon electrolyte of Comparative example4 below) is initially 0.63 V but completely exhausted after the fuelcell runs 600 hours. Judging from these, it is apparent that the unitcell of a fuel cell using an aromatic hydrocarbon electrolyte having asulfonic group bonded to the aromatic ring via an alkyl group is moredurable than the unit cell of a fuel cell using an aromatic hydrocarbonelectrolyte having a sulfonic group directly bonded to the aromaticring. Further, although both membrane/electrode assemblies of Embodiment4 and Comparative example 4 carry 0.25 mg/cm² of platinum, the outputvoltage of Embodiment 4 is greater than the output voltage ofComparative example 4. This is because the ion conductivities of theelectrolyte and the electrode catalyst covering solution in themembrane/electrode assembly of Embodiment 4 are greater than those ofthe electrolyte and the electrode catalyst covering solution in themembrane/electrode assembly of Comparative example 4 and because themembrane/electrode assembly of Embodiment 2 is superior to themembrane/electrode assembly of Comparative example 4.

[0197] (5) Preparation of Fuel Cells

[0198] We piled up 36 unit cells which were prepared in (4) to form asolid polymer electrolyte fuel cell. This fuel cell outputs 3 KW.

COMPARATIVE EXAMPLE 4

[0199] (1) Preparation of Sulfonated Reformed Poly-phenylene Oxide

[0200] We prepared sulfonated reformed poly-phenylene oxide by settingup a 500-ml 4-neck round bottom flask with a reflux condenser, astirrer, a thermometer, and a desiccant tube (containing calciumchloride in it), substituting the air inside the flask by nitrogen gas,putting 12 g of poly-phenylene oxide (m-PPE) and 220 ml ofchlorosulfuric acid, stirring the mixture for 30 minutes at 5° C. in theflow of a nitrogen gas to dissolve PPS, keeping still at 20° C. for 150minutes and at 50° C. for 60 minutes, dripping the reactant solutionslowly into 15 liters of deionized water, filtering the deionized waterto recover the precipitate (sulfonated reformed poly-phenylene oxide),repeating mixing the precipitate with deionized water andsuction-filtering the mixture until the filtrate becomes neutral, andvacuum-drying the precipitate at 80° C. for one night. The ion exchangegroup equivalent weight of the obtained sulfonated reformedpoly-phenylene oxide is 490 g/mol.

[0201] We put 1.0 g of obtained sulfonated reformed poly-phenylene oxideelectrolyte and 20 ml of deionized water in a Teflon-coated hermeticstainless steel container, kept the container at 120° C. for 2 weeks,cooled the container and then measured the ion exchange group equivalentweight of the sulfonated reformed poly-phenylene oxide electrolyte. Asthe result, we found that the ion exchange group equivalent weight ofsulfonated reformed poly-phenylene oxide is 3,500 g/mol which is greaterthan the initial ion exchange group equivalent weight. This means thatthe sulfonic groups are dissociated.

[0202] (2) Preparation of an Electrolyte Membrane

[0203] We prepared a sulfonated reformed poly-phenylene oxideelectrolyte membrane by dissolving the product obtained by the aboveprocedure (1) into a mixture of 20 parts of N,N′-dimethylformamide, 80parts of cyclohexanon, and 25 parts of methylethylketone so that thesolution may contain 5% by weight of the product, spreading thissolution over a glass plate by spin-coating, air-drying thereof, andvacuum-drying thereof at 80° C. The obtained sulfonated reformedpoly-phenylene oxide electrolyte membrane VIII is 45 μm thick and itsion exchange group equivalent is 0.02 S/cm.

[0204] We put said sulfonated reformed poly-phenylene oxide electrolytemembrane VIII and 20 ml of deionized water in a Teflon-coated hermeticstainless steel container and kept the container at 120° C. for 2 weeks.As the result, we found the sulfonated reformed poly-phenylene oxideelectrolyte membrane VIII broken and ragged.

[0205] (3) Preparation of a Solution for Covering Electrode Catalyst anda Membrane/Electrode Assembly

[0206] We prepared a paste (a solution VIII for covering electrodecatalyst) by adding a solvent mixture of N,N′-dimethylformamide,cyclohexanon, and methylethylketone which contains 5% by weight of theproduct (see (2)) to carbon carrying 40% by weight of platinum so thatthe ratio by weight of platinum catalyst and the polymer electrolytemight be 2:1, and dispersing the mixture uniformly. Next we prepared amembrane/electrode assembly VIII by coating both sides of the sulfonatedreformed poly-phenylene oxide electrolyte membrane VIII (obtained by(2)) with said electrode covering solution VIII, and drying thereof.

[0207] The obtained membrane/electrode assembly VIII carries 0.25 mg/cm²of platinum.

[0208] We put said obtained membrane/electrode assembly VIII and 20 mlof deionized water in a Teflon-coated hermetic stainless steel containerand kept the container at 120° C. for 2 weeks. As the result, we foundthe membrane/electrode assembly VIII broken and ragged.

[0209] (4) Endurance Test of Unit Cells of a Fuel Cell

[0210] We prepared a unit cell for a solid polymer electrolyte fuel cellby assembling the membrane/electrode assembly VIII of Comparativeexample 4, thin carbon-paper packing materials (as supporting currentcollectors) in close contact at both sides of the assembly, andconductive separators (bipolar plates) provided at outer sides thereofand also working to separate the electrodes from the chamber and to flowgases to the electrodes and ran the unit cell for a long time at acurrent density of 300 mA/cm². As the result, the output voltage of theunit cell was initially 0.63V but exhausted after a 600-hours run, asshown by the curve 26 in FIG. 9.

[0211] The cost of the sulfopropylated poly-phenylene oxide electrolyteis one fiftieth of the cost of perfluorosulfonic electrolyte which isprepared from expensive material in five processes because thesulfopropylated poly-phenylene oxide electrolyte electrolyte is preparedin a single process from poly-phenylene oxide which is very cheapengineering plastics on-market.

[0212] As seen from Embodiment 4 and Comparative example 4-(1), thearomatic hydrocarbon electrolyte (Embodiment 4) having a sulfonic groupbonded to the aromatic ring via an alkyl group is more resistant to thehot deionized water (120° C.) than the aromatic hydrocarbon electrolyte(Comparative example 3) having a sulfonic group directly bonded to thearomatic ring.

[0213] Referring to Embodiment 4 and Comparative examples 4-(1) and4-(2), although the ion exchange group equivalent weight (520 g/mol) ofEmbodiment 4 (aromatic hydrocarbon electrolyte having a sulfonic groupbonded to the aromatic ring via an alkyl group) is a little greater thanthat (490 g/mol) of Comparative example 4 (aromatic hydrocarbonelectrolyte having a sulfonic group directly bonded to the aromaticring), the ion conductivity of the electrolyte membrane of Embodiment 4is greater than the ion conductivity of the electrolyte membrane ofComparative example 4. (Usually the ion conductivity of an electrolytemembrane is greater as the ion exchange group equivalent weight of theelectrolyte membrane is smaller.) Therefore the electrolyte membrane ofEmbodiment 4 is superior to that of Comparative example 4.

[0214] Referring to Embodiment 4 and Comparative examples 4-(3), theelectrode catalyst covering solution of Embodiment 4 is more suitablefor the aromatic hydrocarbon membrane than the perfluorosulfonicelectrode catalyst covering solution.

[0215] Referring to Embodiment 4 and Comparative examples 4-(4), theoutput voltage of a unit cell using the electrode catalyst coveringsolution of Embodiment 4 is greater than the output voltage of a unitcell using the electrode catalyst covering solution of Comparativeexample 4. Therefore, the electrode catalyst covering solution ofEmbodiment 4 is superior to the electrode catalyst covering solution ofComparative example 4.

[0216] Referring to the curve 24 of FIG. 9, the output voltage of theunit cell of Embodiment 4 is initially 0.82 V and keeps at the samevoltage level even after the unit cell runs 5,000 hours, which is thesame as the behavior of the output voltage of the unit cell using aperfluorosulfonic membrane/electrode assembly (by curve 25). Contrarily,the output of curve 26 (for a unit cell of Comparative example 4) isinitially 0.63 V and completely exhausted after the fuel cell runs 600hours. Judging from these, it is apparent that the unit cell of a fuelcell using an aromatic hydrocarbon electrolyte having a sulfonic groupbonded to the aromatic ring via an alkyl group is more durable than theunit cell of a fuel cell using an aromatic hydrocarbon electrolytehaving a sulfonic group directly bonded to the aromatic ring. Further,although both membrane/electrode assemblies of Embodiment 4 andComparative examples 4 carry 0.25 mg/cm² of platinum, the output voltageof Embodiment 4 is greater than the output voltage of Comparativeexample 4. This is because the ion conductivities of the electrolyte andthe electrode catalyst covering solution in the membrane/electrodeassembly of Embodiment 4 are greater than those of the electrolyte andthe electrode catalyst covering solution in the membrane/electrodeassembly of Comparative example 4 and because the membrane/electrodeassembly of Embodiment 4 is superior to the membrane/electrode assemblyof Comparative example 4.

[0217] [Embodiment 5]

[0218] (1) Preparation of Sulfopropylated Polyether Sulfone

[0219] We prepared sulfopropylated polyether sulfone by setting up a500-ml 4-neck round bottom flask with a reflux condenser, a stirrer, athermometer, and a desiccant tube (containing calcium chloride in it),substituting the air inside the flask by nitrogen gas, putting 11.6 g ofpolyether sulfone (PES), 12.2 g (0.1 mol) of propanesultone and 50 ml ofdry acetophenone in the flask, adding 14.7 g (0.11 mol) of aluminumchloride anhydride to the mixture gradually for 30 minutes whilestirring thereof, refluxing the mixture for 8 hours after addition ofaluminum chloride anhydride is completed, dripping the reactant solutionslowly into 0.5 liter of deionized water, filtering the deionized waterto recover the precipitate (sulfopropylated polyether sulfone),repeating mixing the precipitate with deionized water andsuction-filtering the mixture until the filtrate becomes neutral, andvacuum-drying the precipitate at 120° C. for one night. The ion exchangegroup equivalent weight of the obtained sulfopropylated polyethersulfone is 700 g/mol.

[0220] The cost of the sulfopropylated polyether sulfone electrolyte isone fiftieth or under of the cost of perfluorosulfonic electrolyte whichis prepared from expensive material in five processes because thesulfopropylated polyether sulfone electrolyte is prepared in a singleprocess from poly-ether sulfone which is very cheap engineering plasticson-market.

[0221] We put 1.0 g of obtained sulfopropylated polyether sulfone and 20ml of deionized water in a Teflon-coated hermetic stainless steelcontainer, kept the container at 120° C. for 2 weeks, cooled thecontainer and then measured the ion exchange group equivalent weight ofsulfopropylated polyether sulfone. As the result, we found that the ionexchange group equivalent weight of sulfopropylated polyether sulfoneremains unchanged (700 g/mol) and that sulfopropylated polyether sulfoneis as stable as the expensive perfluorosulfonic electrolyte. Contrarilyas shown by the comparative example 1-(1) below, the cheap sulfonatedaromatic hydrocarbon electrolyte is deteriorated under the sametemperature and hydrolysis condition. Its ion exchange group equivalentincreases up to 3,000 g/mol (which was initially 960 g/mol) and sulfonegroups were dissociated. In other words, the low-cost sulfopropylatedpolyether sulfone electrolyte unlike the cheap sulfonated aromatichydrocarbon electrolyte (see Comparative example I-(1)) shows very goodchemical stability as well as the expensive perfluorosulfonicelectrolyte, satisfying both low cost and high performance.

[0222] (2) Preparation of an Electrolyte Membrane

[0223] We prepared an electrolyte membrane IX by dissolving the productobtained by the above procedure (1) into a solvent solution ofN,N′-dimethyl formamide, spreading this solution over a glass plate byspin-coating, air-drying thereof, and vacuum-drying thereof at 80° C.The obtained electrolyte membrane IX is 40 μm thick.

[0224] We put said obtained electrolyte membrane IX and 20 ml ofdeionized water in a Teflon-coated hermetic stainless steel containerand kept the container at 120° C. for 2 weeks. As the result, we foundthat the ion exchange group equivalent weight of the obtainedelectrolyte membrane IX remains unchanged as well as the expensiveperfluorosulfonic electrolyte. The membrane itself is tough enough.Contrarily as shown by the comparative example 1-(2), the comparativelycheap sulfonated aromatic hydrocarbon electrolyte II is broken andragged under the same temperature and hydrolysis condition. In otherwords, the low-cost sulfopropyl polyethersulfone electrolyte unlike thecheap sulfonated aromatic hydrocarbon electrolyte (see Comparativeexample 1-(2)) shows very good chemical stability as well as theexpensive perfluorosulfonic electrolyte, satisfying both low cost andhigh performance.

[0225] (3) Preparation of a Solution for Covering Electrode Catalyst anda Membrane/Electrode Assembly

[0226] We prepared a solution IX for covering electrode catalyst byadding a N,N′-dimethyl formamide solution to carbon carrying 40% byweight of platinum so that the ratio by weight of platinum catalyst andthe polymer electrolyte might be 2:1, and dispersing the mixtureuniformly. Next we coated one side of the electrolyte membrane IX(obtained by (2)) with said electrode catalyst covering solution IX, anddrying thereof. Further, we prepared a solution IX′ for coveringelectrode catalyst by adding a N,N′-dimethyl formamide solution tocarbon carrying 40% by weight of platinum-ruthenium alloy so that theratio by weight of platinum-ruthenium alloy catalyst and the polymerelectrolyte might be 2:1, and dispersing the mixture uniformly. Next wecovered the other side of the membrane IX (obtained by (2)) with saidelectrode catalyst covering solution IX′, and drying thereof. Thus weprepared a membrane/electrode assembly IX having one side (oxygenelectrode) of 0.29 mg/cm² of platinum and the other side (hydrogenelectrode) of 0.32 mg/cm² of platinum-ruthenium alloy.

[0227] We put said obtained membrane/electrode assembly IX and 20 ml ofdeionized water in a Teflon-coated hermetic stainless steel containerand kept the container at 120° C. for 2 weeks. As the result, we foundthat the obtained electrolyte/membrane assembly IX remains unchanged aswell as the membrane/electrode assembly prepared from the expensiveperfluorosulfonic membrane and the perfluorosulfonic electrolyte. Themembrane itself is tough enough.

[0228] Contrarily as shown by the comparative example 1-(3), themembrane/electrode assembly II prepared by comparatively cheapsulfonated aromatic hydrocarbon electrolyte II and the electrodecatalyst covering solution II is broken and ragged under the sametemperature and hydrolysis condition. In other words, the low-costsulfopropylated polyether sulfone membrane/electrode assembly unlike thecheap sulfonated aromatic hydrocarbon membrane/electrode assembly (seeComparative example 1-(3) is as stable as the expensiveperfluorosulfonic membrane/electrolyte assembly, and satisfies both lowcost and high performance.

[0229] (4) Evaluation of Output of the Unit Cells of a Fuel Cell

[0230] We evaluated the output performance of a fuel cell by dippingsaid membrane/electrode assembly IX in deionized boiling water for 2hours to let the assembly absorb water and setting the wetmembrane/electrode assembly in a sample unit. FIG. 10 shows arelationship between current density and voltage of a unit cell of afuel cell containing membrane/electrode assembly IX. The output voltageof the fuel cell is 0.63 V at a current density of 1 A/cm² and 0.80 V ata current density or 300 mA/cm². This fuel cell is fully available as asolid polymer electrolyte fuel cell.

[0231] We ran the unit cell of said solid polymer electrolyte fuel cellfor a long time at a current density of 300 mA/cm². FIG. 11 shows therelationship between the output voltage and the running time of the unitcell. The curve 27 in FIG. 11 is the result of the endurance test of theunit cell using the membrane/electrode assembly IX in accordance withthe present invention. The curve 28 in FIG. 11 is the result of theendurance test of the unit cell using a perfluorosulfonicmembrane/electrode assembly. As shown by curve 27 in FIG. 11, the outputvoltage of the unit cell is initially 0.80 V and keeps at the samevoltage level even after the unit cell runs 5,000 hours, which is thesame as the behavior of the output voltage of the unit cell using aperfluorosulfonic membrane (by curve 28). As shown by curve 29 in FIG.11, the output voltage (of a unit cell using sulfonated aromatichydrocarbon electrolyte of Comparative example 1 below) is initially0.63 V but completely exhausted after the fuel cell runs 600 hours.Judging from these, it is apparent that the unit cell of a fuel cellusing an aromatic hydrocarbon electrolyte having a sulfonic group bondedto the aromatic ring via an alkyl group is more durable than the unitcell of a fuel cell using an aromatic hydrocarbon electrolyte having asulfonic group directly bonded to the aromatic ring.

[0232] (5) Preparation of Fuel Cells

[0233] We piled up 36 unit cells which were prepared in (5) to form asolid polymer electrolyte fuel cell as that shown in FIG. 3. This fuelcell outputs 3 KW.

[0234] [Embodiment 6]

[0235] (1) Preparation of Sulfopropylated Polysulfone

[0236] We prepared sulfopropylated polysulfone electrolyte by setting upa 500-ml 4-neck round bottom flask with a reflux condenser, a stirrer, athermometer, and a desiccant tube (containing calcium chloride in it),substituting the air inside the flask by nitrogen gas, putting 22.1 g ofpolysulfone (PSU), 12.2 g (0.1 mol) of propanesultone and 50 ml of a drysolvent mixture of tricloroethane-dichloroethane (1:1), adding 14.7 g(0.11 mol) of aluminum chloride anhydride to the mixture gradually for30 minutes while stirring thereof, keeping the mixture at 100° C. for 24hours, dripping the reactant solution into 500 ml of iced watercontaining 25 ml of concentrated hydrochloric acid to stop the reaction,separating the organic precipitate, washing thereof, neutralizingthereof with an aqueous solution of sodium carbonate containing a fewdrops of octyl alcohol, separating aluminum hydroxide by filtration,decoloring the filtrate by active carbon, and evaporating the solvent.The ion exchange group equivalent weight of the obtained sulfopropylatedpolysulfone electrolyte is 750 g/mol.

[0237] The cost of the sulfopropylated sulfone electrolyte is onefiftieth or under of the cost of perfluorosulfonic electrolyte which isprepared from expensive material in five processes because thesulfopropylated sulfone electrolyte is prepared in a single process frompoly-sulfone which is very cheap engineering plastics on-market.

[0238] We put 1.0 g of obtained sulfopropylated polysulfone and 20 ml ofdeionized water in a Teflon-coated hermetic stainless steel container,kept the container at 120° C. for 2 weeks, cooled the container and thenmeasured the ion exchange group equivalent weight of the resiltingsulfopropylated polysulfone electrolyte. As the result, we found thatthe ion exchange group equivalent weight of sulfopropylated sulfoneremains unchanged (750 g/mol) and that sulfopropylated sulfone is asstable as the expensive perfluorosulfonic electrolyte. Contrarily asshown by the comparative example 5-(1) below, the cheap sulfonatedaromatic hydrocarbon electrolyte is deteriorated under the sametemperature and hydrolysis condition. Its ion exchange group equivalentincreases up to 3,000 g/mol (which was initially 700 g/mol) and sulfonegroups were dissociated. In other words, the low-cost sulfopropylatedsulfone electrolyte unlike the cheap sulfonated aromatic hydrocarbonelectrolyte (see Comparative example 5-(1)) shows very good chemicalstability as well as the expensive perfluorosulfonic electrolyte,satisfying both low cost and high performance.

[0239] (2) Preparation of an Electrolyte Membrane

[0240] We prepared an electrolyte membrane by dissolving thesulfopropylated polysulfone electrolyte obtained by the above procedure(1) into a mixture of trichloroethane and dichloroethane (1:1) so thatthe solution may contain 5% by weight of the product, spreading thissolution over a glass plate by spin-coating, air-drying thereof, andvacuum-drying thereof at 80° C. The obtained sulfopropylated polysulfoneelectrolyte membrane X is 42 μm thick.

[0241] We put said obtained sulfopropylated polysulfone electrolytemembrane X and 20 ml of deionized water in a Teflon-coated hermeticstainless steel container, kept the container at 120° C. for 2 weeks,cooled the container and then measured its ion exchange group equivalentweight. As the result, we found that the ion exchange group equivalentweight of the obtained electrolyte membrane remains unchanged as well asthe expensive perfluorosulfonic electrolyte. The membrane itself istough enough. Contrarily as shown by the comparative example 5-(2), thecomparatively cheap sulfonated aromatic hydrocarbon electrolyte XI isbroken and ragged under the same temperature and hydrolysis condition.In other words, the low-cost sulfopropylated polysulfone electrolyteunlike the cheap sulfonated aromatic hydrocarbon electrolyte (seeComparative example 5-(2)) shows very good chemical stability as well asthe expensive perfluorosulfonic electrolyte, satisfying both low costand high performance.

[0242] (3) Preparation of a Solution for Covering Electrode Catalyst anda Membrane/Electrode Assembly

[0243] We prepared a solution X for covering electrode catalyst byadding a solvent mixture of trichloroethaane and dichloroethane (see(2)) to carbon carrying 40% by weight of platinum so that the ratio byweight of platinum catalyst and the polymer electrolyte might be 2:1,and dispersing the mixture uniformly. Next we prepared amembrane/electrode assembly X by coating both sides of the electrolytemembrane X (obtained by (2)) with said solution X for covering electrodecatalyst, and drying thereof. The obtained membrane/electrode assembly Xcarries 0.25 mg/cm² of platinum.

[0244] We put said obtained membrane/electrode assembly X and 20 ml ofdeionized water in a Teflon-coated hermetic stainless steel containerand kept the container at 120° C. for 2 weeks. As the result, we foundthat the ion exchange group equivalent weight of the obtainedelectrolyte membrane remains unchanged as well as the membrane/electrodeassembly prepared from the expensive perfluorosulfonic membrane and theperfluorosulfonic electrolyte. The membrane itself is tough enough.

[0245] Contrarily as shown by the comparative example 5-(3), themembrane/electrode assembly XI prepared by the comparatively cheapsulfonated aromatic hydrocarbon electrolyte XI and the electrodecatalyst covering solution XI is broken and ragged under the sametemperature and hydrolysis condition. In other words, the low-costsulfopropylated sulfon membrane/electrode assembly unlike the cheapsulfonated aromatic hydrocarbon membrane/electrode assembly (seeComparative example 5-(3) is as stable as the expensiveperfluorosulfonic membrane/electrolyte assembly, and satisfies both lowcost and high performance.

[0246] (4) Evaluation of Output of the Unit Cells of a Fuel Cell

[0247] We evaluated the output performance of a fuel cell by dippingsaid membrane/electrode assembly X in deionized boiling water for 2hours to let the assembly absorb water and setting the wetmembrane/electrode assembly X in a sample unit. FIG. 12 shows arelationship between current density and voltage of a unit cell of afuel cell containing membrane/electrode assembly XI. The output voltageof the fuel cell is 0.68 V at a current density of 1 A/cm² and 0.81 V ata current density or 300 mA/cm². This fuel cell is fully available as asolid polymer electrolyte fuel cell.

[0248] We ran the unit cell of said solid polymer electrolyte fuel cellfor a long time at a current density of 300 mA/cm². FIG. 13 shows therelationship between the output voltage and the running time of the unitcell. The curve 30 in FIG. 13 is the result of the endurance test of theunit cell using the membrane/electrode assembly X in accordance with thepresent invention. The curve 31 in FIG. 13 is the result of theendurance test of the unit cell using a perfluorosulfonicmembrane/electrode assembly. As shown by curve 30 in FIG. 13, the outputvoltage of the unit cell is initially 0.81 V and keeps at the samevoltage level even after the unit cell runs 5,000 hours, which is thesame as the behavior of the output voltage of the unit cell using aperfluorosulfonic membrane (by curve 31). As shown by curve 32 in FIG.13, the output voltage (of a unit cell using sulfonated aromatichydrocarbon electrolyte of Comparative example 5 below) is initially0.63 V but completely exhausted after the fuel cell runs 600 hours.Judging from these, it is apparent that the unit cell of a fuel cellusing an aromatic hydrocarbon electrolyte having a sulfonic group bondedto the aromatic ring via an alkyl group is more durable than the unitcell of a fuel cell using an aromatic hydrocarbon electrolyte having asulfonic group directly bonded to the aromatic ring. Further, althoughboth membrane/electrode assemblies of Embodiment 6 and Comparativeexample 5 carry 0.25 mg/cm² of platinum, the output voltage ofEmbodiment 6 is greater than the output voltage of Comparative example5. This is because the ion conductivities of the electrolyte and theelectrode catalyst covering solution in the membrane/electrode assemblyof Embodiment 6 are greater than those of the electrolyte and theelectrode catalyst covering solution in the membrane/electrode assemblyof Comparative example 5 and because the membrane/electrode assembly ofEmbodiment 6 is superior to the membrane/electrode assembly ofComparative example 5.

[0249] (6) Preparation of Fuel Cells

[0250] We piled up 36 unit cells which were prepared in (5) to form asolid polymer electrolyte fuel cell as shown in FIG. 3. This fuel celloutputs 3 KW.

COMPARATIVE EXAMPLE 5

[0251] (1) Preparation of Sulfonated Poly-sulfone

[0252] We prepared sulfonated polyether sulfone by setting up a 500-ml4-neck round bottom flask with a reflux condenser, a stirrer, athermometer, and a desiccant tube (containing calcium chloride in it),substituting the air inside the flask by nitrogen gas, putting 25 g ofpoly-sulfone (PSU) and 125 ml of concentrated sulfuric acid in theflask, stirring the mixture at a room temperature for one night in theflow of nitrogen gas to make a uniform solution, dripping 48 ml ofchlorosulfuric acid first slowly (because the chlorosulfuric acidvigorously reacts with water in the sulfuric acid with bubbles) by adropping funnel into the uniform solution in the flow of nitrogen gas,completing dripping within 5 minutes after bubbling calms down, stirringthe reactant solution at 25° C. for three and half hours to sulfonatethereof, dripping the reactant solution slowly into 15 liters ofdeionized water, filtering the deionized water to recover theprecipitate (sulfonated poly-ethersulfone), repeating mixing theprecipitate with deionized water and suction-filtering the mixture untilthe filtrate becomes neutral, and vacuum-drying the precipitate at 80°C. for one night. The ion exchange group equivalent weight of theobtained sulfonated poly-sulfone electrolyte is 700 g/mol.

[0253] We put 1.0 g of obtained sulfonated polysulfone electrolyte and20 ml of deionized water in a Teflon-coated hermetic stainless steelcontainer, kept the container at 120° C. for 2 weeks, cooled thecontainer and then measured the ion exchange group equivalent weight ofsulfonated polysulfone. As the result, we found that the ion exchangegroup equivalent weight of sulfonated polysulfone electrolyte is 3,000g/mol which is greater than the initial ion exchange group equivalentweight (700 g/mol). This means that the sulfonic groups are dissociated.

[0254] (2) Preparation of an Electrolyte Membrane

[0255] We prepared an electrolyte membrane XI by dissolving sulfonatedpolysulfone electrolyte obtained by the above procedure (1) into amixture of 20 parts of N,N′-dimethylformamide, 80 parts of cyclohexanon,and 25 parts of methylethylketone so that the solution may contain 5% byweight of the product, spreading this solution over a glass plate byspin-coating, air-drying thereof, and vacuum-drying thereof at 80° C.The obtained electrolyte membrane XI is 45 μm thick and its ion exchangegroup equivalent is 0.02 S/cm.

[0256] We put said obtained electrolyte membrane XI and 20 ml ofdeionized water in a Teflon-coated hermetic stainless steel containerand kept the container at 120° C. for 2 weeks. As the result, we foundthe electrolyte membrane XI broken and ragged.

[0257] (3) Preparation of a Solution for Covering Electrode Catalyst anda Membrane/Electrode Assembly

[0258] We prepared a solution XI for covering electrode catalyst byadding a solvent mixture of N,N′-dimethylformamide, cyclohexanon, andmethylethylketone which contains 5% by weight of the product (see (2) tocarbon carrying 40% by weight of platinum so that the ratio by weight ofplatinum catalyst and the polymer electrolyte might be 2:1, anddispersing the mixture uniformly. Next we prepared a membrane/electrodeassembly XI by coating both sides of the electrolyte membrane XI(obtained by (2)) with said solution XI for covering electrode catalyst,and drying thereof. The obtained membrane/electrode assembly XI carries0.25 mg/cm² of platinum.

[0259] We put said obtained membrane/electrode assembly XI and 20 ml ofdeionized water in a Teflon-coated hermetic stainless steel container,kept the container at 120° C. for 2 weeks, cooled the container and theninspected thereof. As the result, we found the membrane/electrodeassembly XI broken and ragged.

[0260] (4) Endurance Test of Unit Cells of a Fuel Cell

[0261] We assembled the membrane/electrode assembly XI of Comparativeexample 5, thin carbon-paper packing materials (as supporting currentcollectors) at both sides of the assembly, and conductive separators(bipolar plates) provided at outer sides thereof and also working toseparate the electrodes from the chamber and to flow gases to theelectrodes into a unit cell for a solid polymer electrolyte fuel cell,and ran the unit cell for a long time at a current density of 300mA/cm². As the result, the output voltage of the unit cell was initially0.68V but exhausted after a 600-hours run, as shown by the curve 32 inFIG. 13.

[0262] [Embodiment 7]

[0263] (1) Preparation of Sulfo-propylated Polysulfone

[0264] We prepared sulfo-propylated poly-sulfone electrolyte by settingup a 500-ml 4-neck round bottom flask with a reflux condenser, astirrer, a thermometer, and a desiccant tube (containing calciumchloride in it), substituting the air inside the flask by nitrogen gas,putting 22.1 g of polysulfone (PSU), 12.2 g (0.1 mol) of propane-sultoneand 50 ml of dry nitrobenzene, adding 14.7 g (0.11 mol) of aluminumchloride anhydride to the mixture gradually for 30 minutes whilestirring thereof, then refluxing for 24 hours, dripping the reactantsolution into 500 ml of iced water containing 25 ml of concentratedhydrochloric acid to stop the reaction, separating the organicprecipitate, washing thereof, neutralizing thereof with an aqueoussolution of sodium carbonate containing a few drops of octyl alcohol,separating aluminum hydroxide by filtration, decoloring the filtrate byactive carbon, and evaporating the solvent. The ion exchange groupequivalent weight of the obtained sulfo-propylated polysulfoneelectrolyte is 660 g/mol.

[0265] The cost of the sulfo-propylated sulfone electrolyte is onefiftieth or under of the cost of perfluoro-sulfonic electrolyte which isprepared from expensive material in five processes because thesulfo-propylated sulfone electrolyte is prepared in a single processfrom poly-sulfone which is very cheap engineering plastics on-market.

[0266] We put 1.0 g of obtained sulfo-propylated polysulfone and 20 mlof deionized water in a Teflon-coated hermetic stainless steelcontainer, kept the container at 120° C. for 2 weeks, cooled thecontainer and then measured the ion exchange group equivalent weight ofthe resilting sulfo-propylated polysulfone electrolyte. As the result,we found that the ion exchange group equivalent weight ofsulfo-propylated sulfone remains unchanged (660 g/mol) and thatsulfo-propylated sulfone is as stable as the expensiveperfluoro-sulfonic electrolyte. Contrarily as shown by the comparativeexample 5-(1) below, the cheap sulfonated aromatic hydrocarbonelectrolyte is deteriorated under the same temperature and hydrolysiscondition. Its ion exchange group equivalent increases up to 3,000 g/mol(which was initially 700 g/mol) and sulfone groups were dissociated. Inother words, the low-cost sulfo-propylated sulfone electrolyte unlikethe cheap sulfonated aromatic hydrocarbon electrolyte (see Comparativeexample 5-(1)) shows very good chemical stability as well as theexpensive perfluoro-sulfonic electrolyte, satisfying both low cost andhigh performance.

[0267] (2) Preparation of an Electrolyte Membrane

[0268] We prepared an electrolyte membrane by dissolving the productobtained by the above procedure (1) into a mixture of trichloroethaneand dichloroethane (1:1) so that the solution may contain 5% by weightof the product, spreading this solution over a glass plate byspin-coating, air-drying thereof, and vacuum-drying thereof at 80° C.The obtained sulfo-propylated poly-sulfone electrolyte membrane X is 38μm thick.

[0269] We put said obtained sulfo-propylated poly-sulfone electrolytemembrane X and 20 ml of deionized water in a Teflon-coated hermeticstainless steel container, kept the container at 120° C. for 2 weeks,cooled the container and then measured its ion exchange group equivalentweight. As the result, we found that the ion exchange group equivalentweight of the obtained electrolyte membrane remains unchanged as well asthe expensive perfluoro-sulfonic electrolyte. The membrane itself istough enough. Contrarily as shown by the comparative example 5-(2), thecomparatively cheap sulfonated aromatic hydrocarbon electrolyte XI isbroken and ragged under the same temperature and hydrolysis condition.In other words, the low-cost sulfo-propylated poly-sulfone electrolyteunlike the cheap sulfonated aromatic hydrocarbon electrolyte (seeComparative example 5-(2)) shows very good chemical stability as well asthe expensive perfluoro-sulfonic electrolyte, satisfying both low costand high performance.

[0270] (3) Preparation of a Solution for Covering Electrode Catalyst anda Membrane/Electrode Assembly

[0271] We prepared a solution for covering electrode catalyst by addinga solvent mixture of trichloro-ethaane and dichloro-ethane (see (2)) tocarbon carrying 40% by weight of platinum so that the ratio by weight ofplatinum catalyst and the polymer electrolyte might be 2:1, anddispersing the mixture uniformly. Next we prepared a membrane/electrodeassembly by coating both sides of the electrolyte membrane (obtained by(2)) with said solution for covering electrode catalyst, and dryingthereof. The obtained membrane/electrode assembly carries 0.25 mg/cm² ofplatinum.

[0272] We put said obtained membrane/electrode assembly and 20 ml ofdeionized water in a Teflon-coated hermetic stainless steel containerand kept the container at 120° C. for 2 weeks. As the result, we foundthat the ion exchange group equivalent weight of the obtainedelectrolyte membrane remains unchanged as well as the membrane/electrodeassembly prepared from the expensive perfluoro-sulfonic membrane and theperfluoro-sulfonic electrolyte. The membrane itself is tough enough.

[0273] Contrarily as shown by the comparative example 5-(3), themembrane/electrode assembly prepared by the comparatively cheapsulfonated aromatic hydrocarbon electrolyte and the electrode catalystcovering solution is broken and ragged under the same temperature andhydrolysis condition. In other words, the low-cost sulfo-propylatedsulfon membrane/electrode assembly unlike the cheap sulfonated aromatichydrocarbon membrane/electrode assembly (see Comparative example 5-(3)is as stable as the expensive perfluoro-sulfonic membrane/electrolyteassembly, and satisfies both low cost and high performance.

[0274] (4) Evaluation of Output of the Unit Cells of a Fuel Cell

[0275] We evaluated the output performance of a fuel cell by dippingsaid membrane/electrode assembly in deionized boiling water for 2 hoursto let the assembly absorb water and setting the wet membrane/electrodeassembly in a sample unit. FIG. 14 shows a relationship between currentdensity and voltage of a unit cell of a fuel cell containingmembrane/electrode assembly. The output voltage of the fuel cell is 0.75V at a current density of 1 A/cm² and 0.83 V at a current density or 300mA/cm². This fuel cell is fully available as a solid polymer electrolytefuel cell.

[0276] We ran the unit cell of said solid polymer electrolyte fuel cellfor a long time at a current density of 300 mA/cm². FIG. 15 shows therelationship between the output voltage and the running time of the unitcell. The curve 33 in FIG. 15 is the result of the endurance test of theunit cell using the membrane/electrode assembly in accordance with thepresent invention. The curve 34 in FIG. 15 is the result of theendurance test of the unit cell using a perfluoro-sulfonicmembrane/electrode assembly. As shown by curve 33 in FIG. 15, the outputvoltage of the unit cell is initially 0.83 V and keeps at the samevoltage level even after the unit cell runs 5,000 hours, which is thesame as the behavior of the output voltage of the unit cell using aperfluoro-sulfonic membrane (by curve 34). As shown by curve 35 in FIG.15, the output voltage (of a unit cell using sulfonated aromatichydrocarbon electrolyte of Comparative example 5 below) is initially0.63 V but completely exhausted after the fuel cell runs 600 hours.Judging from these, it is apparent that the unit cell of a fuel cellusing an aromatic hydrocarbon electrolyte having a sulfonic group bondedto the aromatic ring via an alkyl group is more durable than the unitcell of a fuel cell using an aromatic hydrocarbon electrolyte having asulfonic group directly bonded to the aromatic ring. Further, althoughboth membrane/electrode assemblies of Embodiment 7 and Comparativeexample 5 carry 0.25 mg/cm² of platinum, the output voltage ofEmbodiment 7 is greater than the output voltage of Comparative example5. This is because the ion conductivities of the electrolyte and theelectrode catalyst covering solution in the membrane/electrode assemblyof Embodiment 7 are greater than those of the electrolyte and theelectrode catalyst covering solution in the membrane/electrode assemblyof Comparative example 5 and because the membrane/electrode assembly ofEmbodiment 7 is superior to the membrane/electrode assembly ofComparative example 5.

[0277] (6) Preparation of Fuel Cells

[0278] We piled up 36 unit cells which were prepared in (5) to form asolid polymer electrolyte fuel cell as shown in FIG. 3. This fuel celloutputs 3 KW.

[0279] [Embodiment 8 to Embodiment 13]

[0280] We prepared sulfo-alkylated aromatic hydrocarbon electrolyte bysetting up a 500-ml 4-neck round bottom flask with a reflux condenser, astirrer, a thermometer, and a desiccant tube (containing calciumchloride in it), substituting the air inside the flask by nitrogen gas,putting an aromatic hydrocarbon polymer, a sultone, and 50 ml of drynitrobenzene in the flask, adding 14.7 g (0.11 mol) of aluminum chlorideanhydride to the mixture gradually for 30 minutes while stirringthereof, refluxing the mixture at a preset temperature for a preset timeperiod after addition of aluminum chloride anhydride is completed,pouring the reactant into 150 ml of iced water containing 25 ml ofconcentrated hydrochloric acid to stop the reaction, dripping thereactant solution slowly into 0.5 liter of deionized water, filteringthe deionized water to recover the precipitate (sulfo-alkylated aromatichydrocarbon), repeating mixing the precipitate with deionized water andsuction-filtering the mixture until the filtrate becomes neutral, andvacuum-drying the precipitate at 120° C. for one night. We measured andevaluated the water resistance, and deterioration of the electrolyte andthe membrane/electrode assembly, and performance of the unit cell of afuel cell made thereof. Table 1 shows the result of evaluation andmeasurement. The cost of the sulfo-alkylated aromatic hydrocarbonelectrolyte is one fortieth or under of the cost of perfluoro-sulfonicelectrolyte which is prepared from expensive material in five processesbecause the sulfo-alkylated aromatic hydrocarbon electrolyte is preparedin a single process from very cheap engineering plastics on-market. Weput respective sulfo-alkylated aromatic hydrocarbon electrolytes ofEmbodiment 8 to Embodiment 13 and deionized water in a Teflon-coatedhermetic stainless steel container, kept each container at 120° C. for 2weeks, and measured the ion exchange group equivalent weight of eachsulfo-alkylated aromatic hydrocarbon electrolytes. As the result, wefound that each of sulfo-alkylated aromatic hydrocarbon electrolytesunlike the cheap sulfonated aromatic hydrocarbon of Comparative example1 keeps its initial value and is as stable as the expensiveperfluoro-sulfonic electrolyte, satisfying the low cost and highperformance. We put respective sulfo-alkylated aromatic hydrocarbonelectrolytes of Embodiment 8 to Embodiment 13 and deionized water in aTeflon-coated hermetic stainless steel container, kept each container at120° C. for 2 weeks, and measured the ion exchange group equivalentweight of each sulfo-alkylated aromatic hydrocarbon electrolytes. As theresult, we found that each of sulfo-alkylated aromatic hydrocarbonelectrolytes unlike the cheap sulfonated aromatic hydrocarbon ofComparative example 1 keeps its original shape and is as stable as theexpensive perfluoro-sulfonic electrolyte, satisfying the low cost andhigh performance. We put respective sulfo-alkylated aromatic hydrocarbonmembrane/electrode assemblies of Embodiment 8 to Embodiment 13 anddeionized water in a Teflon-coated hermetic stainless steel containerand kept each container at 120° C. for 2 weeks. We found that each ofthe sulfo-alkylated aromatic hydrocarbon membrane/electrode assembliesunlike the sulfonated aromatic hydrocarbon of Comparative example 1keeps its original property and is as stable as the expensiveperfluoro-sulfonic membrane/electrode assembly, satisfying the low costand high performance. Further after running respective unit cells at 300mA/cm² for 5,000 hours, we found that the output of respective unitcells using sulfo-alkylated aromatic hydrocarbon electrolytes unlike theoutput of a unit cell using the sulfonated aromatic hydrocarbonelectrolyte of Comparative example 1 keeps the initial output voltageand is as stable as the unit cell using the expensive perfluoro-sulfonicelectrolyte, satisfying the low cost and high performance. TABLE 1Embodiment Embodiment Embodiment Embodiment Embodiment Embodiment 8 9 1011 12 13 Aromatic hydrocarbon Poly-allyl- Poly-ketone Poly-ether-Poly-ether- Poly-ether- Poly-ether- polymer (g) ether- (12.0) ketonesulfone sulfone sulfone (14.0) (15.0) (20.0) (5.0) (11.6) Sultone (g)Propane- Propane- Propane- Propane- Propane- Butane- sultone sultonesultone sultone sultone sultone (12.2) (12.2) (12.2) (12.2) (25.5)(13.6) Temperature of reaction 150 150 150 150 150 150 (° C.) Time ofreaction (hr) 12 12 12 5 30 30 Ion exchange group 620 610 680 1000 250680 equivalent weight (g/mol) Ion exchange group 620 610 680 1000 250680 equivalent weight of electrolyte after dipping in deionized water at120° C. for 2 weeks (g/mol) Ion exchange group No change No change Nochange No change No change No change equivalent weight of membrane afterdipping in deionized water at 120° C. for 2 weeks Ion exchange group Nochange No change No change No change No change No change equivalentweight of membrane/electrode assembly after dipping in deionized waterat 120° C. for 2 weeks Initial output of unit 0.65 0.66 0.65 0.6 0.690.65 cell (V at 1A/cm²) Output of unit cell 97 98 96 97 96 95 afterrunning at 300 mA/cm² for 5,000 hours (ratio to the initial voltage inpercentage)

[0281] [Embodiment 14]

[0282] (1) Preparation of Chloromethylated Poly-ether Sulfone

[0283] We prepared chloromethylated poly-ether sulfone by setting up a500-ml 4-neck round bottom flask with a reflux condenser, a stirrer, athermometer, and a desiccant tube (containing calcium chloride in it),substituting the air inside the flask by nitrogen gas, putting 21.6 g ofpoly-ether sulfone (PES), 60 g (2 moles) of paraformaldehyde and 50 mlof dry nitro benzene, blowing 73 g of hydrogen chloride gas whilestirring at 100° C., keeping the mixture at 150° C., dripping thereactant solution slowly into 1 liter of deionized water, lettingchloromethylated poly-ether sulfone deposit, filtrating and recoveringthe precipitate repeating mixing the precipitate with deionized waterand suction-filtering the mixture until the filtrate becomes neutral,and vacuum-drying the precipitate at 80° C. for one night.

[0284] (2) Preparation of Sulfo-methylated Poly-ether Sulfone W

[0285] e prepared sulfo-methylated poly-ether sulfone by setting up a500-ml 4-neck round bottom flask with a reflux condenser, a stirrer, athermometer, and a desiccant tube (containing calcium chloride in it),substituting the air inside the flask by nitrogen gas, putting 10 g ofchloro-methylated poly-ether sulfone, 50 ml of dry nitro benzene, and 30g of sodium sulfate, stirring the mixture at 100° C. for 5 hours, adding10 ml of deionized water, stirring the solution for five hours, drippinga reactant solution slowly into 1 liter of deionized water, lettingsulfo-methylated poly-ether sulfone deposit, filtrating and recoveringthe precipitate repeating mixing the precipitate with deionized waterand suction-filtering the mixture until the filtrate becomes neutral,and vacuum-drying the precipitate at 120° C. for one night. The ionexchange group equivalent weight of the resulting sulfo-methylatedpoly-ether sulfone electrolyte is 600 g/mol.

[0286] As the sulfo-methylated poly-ether sulfone electrolyte inaccordance with the present invention can be produced in two processesfrom poly-poly-ether-sulfone which is inexpensive engineering plasticson-market, the cost of the sulfo-methylated poly-ether sulfoneelectrolyte is one thirtieth or under of the perfluorosulfonicelectrolyte which is produced in five processes from expensivematerials. However, the method of producing the sulfoalkylatedpoly-ether sulfone electrolyte by sulfoalkylatingpoly-poly-ether-sulfone directly by sultone (as in Embodiment 1) has oneprocess less than the method of Embodiment 14. Therefore the cost of thesulfoalkylated poly-ether sulfone electrolyte is two third of the costof product obtained by the method of Embodiment 14. Namely, the methodof sulfoalkylating sulfoalkylating poly-poly-ether-sulfone directly bysultone is lower-costed.

[0287] We put 1.0 g of the obtained sulfo-methylated poly-ether sulfoneelectrolyte and 20 ml of deionized water in a Teflon-coated hermeticstainless steel container, kept the container at 120° C. for 2 weeks,cooled the container and then measured the ion exchange group equivalentweight of sulfo-methylated poly-ether sulfone electrolyte. As theresult, we found that the ion exchange group equivalent weight of thesulfopropylated polyether sulfone electrolyte remains unchanged (600g/mol) and that sulfopropylated polyether sulfone is as stable as theexpensive perfluorosulfonic electrolyte. Contrarily as shown by theComparative example 1-(1) below, the cheap sulfonated aromatichydrocarbon electrolyte is deteriorated under the same temperature andhydrolysis condition. Its ion exchange group equivalent increases up to3,000 g/mol (which was initially 960 g/mol) and sulfone groups weredissociated. In other words, the low-cost sulfo-methylated poly-ethersulfone electrolyte unlike the cheap sulfonated aromatic hydrocarbonelectrolyte shows very good chemical stability as well as the expensiveperfluorosulfonic electrolyte, satisfying both low cost and highperformance.

[0288] (3) Preparation of an electrolyte membrane

[0289] We prepared an electrolyte membrane by dissolving thesulfo-methylated poly-ether-sulfone electrolyte obtained by the aboveprocedure (2) into a mixture of trichloroethane and dichloroethane (1:1)so that the solution may contain 5% by weight of the product, spreadingthis solution over a glass plate by spin-coating, air-drying thereof,and vacuum-drying thereof at 80° C. The obtained sulfo-methylatedpoly-ether-sulfone electrolyte membrane is 42 μm thick.

[0290] We put said obtained sulfo-methylated poly-ether-sulfoneelectrolyte membrane and 20 ml of deionized water in a Teflon-coatedhermetic stainless steel container and kept the container at 120° C. for2 weeks. As the result, we found that the ion exchange group equivalentweight of the obtained electrolyte membrane remains unchanged as well asthe expensive perfluoro-sulfonic electrolyte. The membrane itself istough enough. Contrarily as shown by the comparative example 1-(2), thecomparatively cheap sulfonated aromatic hydrocarbon electrolyte isbroken and ragged under the same temperature and hydrolysis condition.In other words, the low-cost sulfo-methylated poly-ether-sulfoneelectrolyte unlike the cheap sulfonated aromatic hydrocarbon electrolyteshows very good chemical stability as well as the expensiveperfluoro-sulfonic electrolyte, satisfying both low cost and highperformance.

[0291] (4) Preparation of a Solution for Covering Electrode Catalyst anda Membrane/Electrode Assembly

[0292] We prepared a paste (solution for covering electrode catalyst) byadding a solvent mixture of trichloro-ethaane and di-chloro-ethane (see(3)) to carbon carrying 40% by weight of platinum so that the ratio byweight of platinum catalyst and the polymer electrolyte might be 2:1,and dispersing the mixture uniformly. Next we prepared amembrane/electrode assembly by coating both sides of the electrolytemembrane (obtained by (2)) with said solution for covering electrodecatalyst, and drying thereof. The obtained membrane/electrode assemblycarries 0.25 mg/cm² of platinum.

[0293] We put the obtained membrane/electrode assembly and 20 ml ofdeionized water in a Teflon-coated hermetic stainless steel containerand kept the container at 120° C. for 2 weeks. As the result, we foundthat the property of the membrane/electrode assembly keeps its initialproperty as well as the expensive perfluoro-sulfonic membrane/electrodeassembly prepared by the expensive perfluoro-sulfonic membrane and theperfluoro-sulfonic electrolyte. Its membrane is tough enough.

[0294] Contrarily as shown by the comparative example 1-(3), themembrane/electrode assembly prepared by the comparatively cheapsulfonated aromatic hydrocarbon electrolyte membrane II and theelectrode catalyst covering solution II is deteriorated under the sametemperature and hydrolysis condition. The electrodes are separated fromthe assembly. In other words, the low-cost sulfomethylated polyethersulfone membrane/electrode assembly unlike the cheap sulfonated aromatichydrocarbon membrane/electrode assembly (see Comparative example I-(3))shows very good chemical stability as well as the expensiveperfluoro-sulfonic electrolyte, satisfying both low cost and highperformance.

[0295] (5) Evaluation of Output of the Unit Cells of a Fuel Cell

[0296] We evaluated the output performance of a fuel cell by dippingsaid membrane/electrode assembly in deionized boiling water for 2 hoursto let the assembly absorb water and setting the wet membrane/electrodeassembly in a sample unit. FIG. 16 shows a relationship between currentdensity and voltage of a unit cell of a fuel cell containingmembrane/electrode assembly. The output voltage of the fuel cell is 0.68V at a current density of 1 A/cm² and 0.82 V at a current density or 300mA/cm². This fuel cell is fully available as a solid polymer electrolytefuel cell.

[0297] We ran the unit cell of said solid polymer electrolyte fuel cellfor a long time at a current density of 300 mA/cm². FIG. 17 shows therelationship between the output voltage and the running time of the unitcell. The curve 36 in FIG. 17 is the result of the endurance test of theunit cell using the membrane/electrode assembly in accordance with thepresent invention. The curve 37 in FIG. 17 is the result of theendurance test of the unit cell using a perfluoro-sulfonicmembrane/electrode assembly. As shown by curve 36 in FIG. 17, the outputvoltage of the unit cell is initially 0.82 V and keeps at the samevoltage level even after the unit cell runs 5,000 hours, which is thesame as the behavior of the output voltage of the unit cell using aperfluoro-sulfonic membrane (by curve 37). As shown by curve 38 in FIG.17, the output voltage (of a unit cell using sulfonated aromatichydrocarbon electrolyte of Comparative example) is initially 0.73 V butcompletely exhausted after the fuel cell runs 600 hours. Judging fromthese, it is apparent that the unit cell of a fuel cell using anaromatic hydrocarbon electrolyte having a sulfonic group bonded to thearomatic ring via an alkyl group is more durable than the unit cell of afuel cell using an aromatic hydrocarbon electrolyte having a sulfonicgroup directly bonded to the aromatic ring. Further, although bothmembrane/electrode assemblies of Embodiment 14 and Comparative example 1carry 0.25 mg/cm² of platinum, the output voltage of Embodiment 14 isgreater than the output voltage of Comparative example 4. This isbecause the ion conductivities of the electrolyte and the electrodecatalyst covering solution in the membrane/electrode assembly ofEmbodiment 14 are greater than those of the electrolyte and theelectrode catalyst covering solution in the membrane/electrode assemblyof Comparative example 1 and because the membrane/electrode assembly ofEmbodiment 14 is superior to the membrane/electrode assembly ofComparative example 1.

[0298] (6) Preparation of Fuel Cells

[0299] We piled up 36 unit cells which were prepared in (5) to form asolid polymer electrolyte fuel cell as that shown in FIG. 3. This fuelcell outputs 3 KW.

[0300] [Embodiment 15]

[0301] (1) Preparation of Bromo-hexamethylated Poly-ether Sulfone

[0302] We prepared bromo-hexamethylated poly-ether sulfone by setting upa 500-ml 4-neck round bottom flask with a reflux condenser, a stirrer, athermometer, and a desiccant tube (containing calcium chloride in it),substituting the air inside the flask by nitrogen gas, putting 23.2 g ofpolyether sulfone (PES) and 50 ml of dry nitrobenzene in the flask,adding 6.5 g of butoxylithium to the mixture, keeping the mixture at theroom temperature for 2 hours, adding 100 g of 1,6-dibromohexane to themixture, stirring thereof for 12 hours, dripping the reactant solutionslowly into 1 liter of deionized water, filtering the deionized water torecover the precipitate (bromo-hexamethylated poly-ether sulfone),repeating mixing the precipitate with deionized water andsuction-filtering the mixture until the filtrate becomes neutral, andvacuum-drying the precipitate at 120° C. for one night.

[0303] (2) Preparation of Sulfo-hexamethylated Poly-ether Sulfone

[0304] We prepared sulfo-hexamethylated poly-ether sulfone by setting upa 500-ml 4-neck round bottom flask with a reflux condenser, a stirrer, athermometer, and a desiccant tube (containing calcium chloride in it),substituting the air inside the flask by nitrogen gas, putting 10 g ofbromo-hexamethylated poly-ether sulfone, 50 ml of dry nitrobenzene, and30 g of sodium sulfate in the flask, stirring the mixture at 100° C. for5 hours, adding 10 ml of eionized water to the mixture, stirring themixture for 5 hours, dripping the reactant solution slowly into 1 literof deionized water, filtering the deionized water to recover theprecipitate (sulfo-hexamethylated poly-ether sulfone), repeating mixingthe precipitate with deionized water and suction-filtering the mixtureuntil the filtrate becomes neutral, and vacuum-drying the precipitate at120° C. for one night. The ion exchange group equivalent weight of theobtained sulfo-hexamethylated poly-ether sulfone is 600 g/mol.

[0305] The cost of the sulfoalkylated poly-ether sulfone electrolyte inthe present method is one thirtieth or under of the cost ofperfluoro-sulfonic electrolyte which is prepared from expensivematerials in five processes because the sulfoalkylated poly-ethersulfone electrolyte is prepared in a two processes frompoly-poly-ether-sulfone which is very cheap engineering plasticson-market. However, the method of producing the sulfoalkylatedpoly-ether sulfone electrolyte by sulfoalkylatingpoly-poly-ether-sulfone directly by sultone (as in Embodiment 1) has oneprocess less than the method of Embodiment 14. Therefore the cost of thesulfoalkylated poly-ether sulfone electrolyte is two third of the costof product obtained by the method of Embodiment 14. Namely, the methodof sulfoalkylating sulfoalkylating poly-poly-ether-sulfone directly bysultone is lower-costed.

[0306] We put 1.0 g of the obtained sulfo-hexamethylated poly-ethersulfone electrolyte and 20 ml of deionized water in a Teflon-coatedhermetic stainless steel container, kept the container at 120° C. for 2weeks, cooled the container and then measured the ion exchange groupequivalent weight of sulfo-hexamethylated poly-ether sulfoneelectrolyte. As the result, we found that the ion exchange groupequivalent weight of the sulfo-hexamethylated polyether sulfoneelectrolyte remains unchanged (600 g/mol) and that sulfopropylatedpolyether sulfone is as stable as the expensive perfluorosulfonicelectrolyte. Contrarily as shown by the Comparative example 1-(1) below,the cheap sulfonated aromatic hydrocarbon electrolyte is deterioratedunder the same temperature and hydrolysis condition. Its ion exchangegroup equivalent increases up to 3,000 g/mol (which was initially 960g/mol) and sulfone groups were dissociated. In other words, the low-costsulfo-hexamethylated poly-ether sulfone electrolyte unlike the cheapsulfonated aromatic hydrocarbon electrolyte shows very good chemicalstability as well as the expensive perfluorosulfonic electrolyte,satisfying both low cost and high performance.

[0307] (3) Preparation of an Electrolyte Membrane

[0308] We prepared an electrolyte membrane by dissolving the productobtained in the above procedure (2) into a mixture of 20 parts ofN,N′-dimethylformamide, 80 parts of cyclohexanon, and 25 parts ofmethylethylketone so that the solution may contain 5% by weight of theproduct, spreading this solution over a glass plate by spin-coating,air-drying thereof, and vacuum-drying thereof at 80° C. The obtainedsulfo-hexamethylated poly-ether sulfone electrolyte membrane is 42 μmthick and its ion exchange group equivalent is 8 S/cm.

[0309] We put the obtained sulfo-hexamethylated poly-ether sulfoneelectrolyte membrane and 20 ml of deionized water in a Teflon-coatedhermetic stainless steel container and kept the container at 120° C. for2 weeks. As the result, we found that the ion exchange group equivalentweight of the product remains unchanged and is as stable as theexpensive perfluoro-sulfonic electrolyte. Its membrane is tough enough.Contrarily as shown by the comparative example 1-(2) below, the cheapsulfonated aromatic hydrocarbon electrolyte is broken and ragged underthe same temperature and hydrolysis condition. In other words, thelow-cost sulfo-hexamethylated poly-ether sulfone electrolyte membraneunlike the cheap sulfonated aromatic hydrocarbon electrolyte shows verygood chemical stability as well as the expensive perfluoro-sulfonicelectrolyte, satisfying both low cost and high performance.

[0310] (4) Preparation of an Electrolyte Membrane

[0311] We prepared a paste (an electrolyte catalyst covering solution)by dissolving the product (3) into a mixture of trichloroethane anddichloroethane, adding this mixture to carbon carrying 40% by weight ofplatinum so that the weight ration of platinum catalyst and polymerelectrolyte may be 2:1, and dispersing thereof uniformly. Next weprepared a membrane/electrode assembly by coating both sides of theelectrolyte membrane (obtained by (3)) with said electrode coveringsolution, and drying thereof. The obtained membrane/electrode assemblycarries 0.25 mg/cm² of platinum.

[0312] We put the obtained sulfo-hexamethylated poly-ether sulfoneelectrolyte membrane and 20 ml of deionized water in a Teflon-coatedhermetic stainless steel container and kept the container at 120° C. for2 weeks. As the result, we found that the resulting membrane/electrodeassembly remains unchanged and is as stable as the membrane/electrodeassembly made from the expensive perfluoro-sulfonic membrane and theperfluoro-sulfonic electrolyte. Its membrane is tough enough. Contrarilyas shown by the comparative example 1-(3) below, the cheap sulfonatedaromatic hydrocarbon electrolyte II prepared by the comparatively cheapsulfonated aromatic hydrocarbon electrolyte membrane II and theelectrolyte catalyst covering solution II is broken and ragged under thesame temperature and hydrolysis conditions and the electrodes areseparated from the assembly. In other words, the low-costsulfo-hexametylated polyether sulfone membrane/electrode assembly unlikethe cheap sulfonated aromatic hydrocarbon electrolyte (see Comparativeexample I-(3)) shows very good chemical stability as well as theexpensive perfluoro-sulfonic membrane/electrode assembly, satisfyingboth low cost and high performance.

[0313] (5) Evaluation of Output of the Unit Cells of a Fuel Cell

[0314] We evaluated the output performance of a fuel cell by dippingsaid membrane/electrode assembly in deionized boiling water for 2 hoursto let the assembly absorb water and setting the wet membrane/electrodeassembly in a sample unit. FIG. 18 shows a relationship between currentdensity and voltage of a unit cell of a fuel cell containingmembrane/electrode assembly. The output voltage of the fuel cell is 0.68V at a current density of 1 A/cm² and 0.83 V at a current density or 300mA/cm². This fuel cell is fully available as a solid polymer electrolytefuel cell.

[0315] We ran the unit cell of said solid polymer electrolyte fuel cellfor a long time at a current density of 300 MA/cm². FIG. 19 shows therelationship between the output voltage and the running time of the unitcell. The curve 39 in FIG. 19 is the result of the endurance test of theunit cell using the membrane/electrode assembly in accordance with thepresent invention. The curve 40 in FIG. 19 is the result of theendurance test of the unit cell using a perfluoro-sulfonicmembrane/electrode assembly. As shown by curve 39 in FIG. 19, the outputvoltage of the unit cell is initially 0.83 V and keeps at the samevoltage level even after the unit cell runs 5,000 hours, which is thesame as the behavior of the output voltage of the unit cell using aperfluoro-sulfonic membrane (by curve 40). As shown by curve 41 in FIG.19, the output voltage (of a unit cell using sulfonated aromatichydrocarbon electrolyte of Comparative example 1) is initially 0.73 Vbut completely exhausted after the fuel cell runs 600 hours. Judgingfrom these, it is apparent that the unit cell of a fuel cell using anaromatic hydrocarbon electrolyte having a sulfonic group bonded to thearomatic ring via an alkyl group is more durable than the unit cell of afuel cell using an aromatic hydrocarbon electrolyte having a sulfonicgroup directly bonded to the aromatic ring. Further, although bothmembrane/electrode assemblies of Embodiment 15 and Comparative example 1carry 0.25 mg/cm² of platinum, the output voltage of Embodiment 15 isgreater than the output voltage of Comparative example 4. This isbecause the ion conductivities of the electrolyte and the electrodecatalyst covering solution in the membrane/electrode assembly ofEmbodiment 15 are greater than those of the electrolyte and theelectrode catalyst covering solution in the membrane/electrode assemblyof Comparative example 1 and because the membrane/electrode assembly ofEmbodiment 15 is superior to the membrane/electrode assembly ofComparative example 1.

[0316] (6) Preparation of Fuel Cells

[0317] We piled up 36 unit cells which were prepared in (5) to form asolid polymer electrolyte fuel cell as that shown in FIG. 3. This fuelcell outputs 3 KW.

[0318] [Effect of the Invention]

[0319] The sulfoalkylated aromatic hydrocarbon electrolyte in accordancewith the present invention can be produced in a single process fromlow-cost engineering plastics and its cost is one fortieth or under of afluorine electrolyte membrane represented by a perfluoro-sulfonicmembrane which is produced in five processes from expensive materials.Further due to the bonding of a sulfonic group to a benzene ring via analkyl group unlike the direct bonding of a sulfonic group to a benzenering, the ion conductivity of the sulfoalkylated aromatic hydrocarbonelectrolyte is great, suppresses sulfonic groups from being dissociatedat a high temperature in the presence of a strong acid, and shows asubstantially high chemical durability. Therefore, electrolytemembranes, electrolyte catalyst covering solutions, membrane/electrodeassemblies, and fuel cells using the sulfoalkylated aromatic hydrocarbonelectrolyte in accordance with the present invention show asubstantially high chemical durability and can reduce steps ofproduction.

What is claimed is:
 1. A solid polymer electrolyte comprising aromatichydrocarbon polymer compound having a sulfoalkyl group expressed byFORMULA 1 as a side chain. U.S. Pat. No. Formula 1

(wherein “n” is 1, 2, 3, 4, 5, or 6.)
 2. A solid polymer electrolyte inaccordance with claim 1, wherein said aromatic hydrocarbon polymercompound is poly-ether sulfonic polymer compound.
 3. A solid polymerelectrolyte in accordance with claim 1, wherein said aromatichydrocarbon polymer compound is poly-ether ether ketone polymercompound.
 4. A solid polymer electrolyte in accordance with claim 1,wherein said aromatic hydrocarbon polymer compound is poly-phenylenesulfide polymer compound.
 5. A solid polymer electrolyte in accordancewith claim 1, wherein said aromatic hydrocarbon polymer compound ispoly-phenylene ether polymer compound.
 6. A solid polymer electrolyte inaccordance with claim 1, wherein said aromatic hydrocarbon polymercompound is poly-ether sulfonic polymer compound.
 7. A solid polymerelectrolyte in accordance with claim 1, wherein said aromatichydrocarbon polymer compound is poly-ether ketone polymer compound.
 8. Apolymer electric membrane containing a solid polymer electrolyte inaccordance with any of claims 1 to
 7. 9. A solution for coatingelectrode catalyst binding fine catalytic metal particles to the surfaceof a conductive material made of carbon with a binder, wherein saidsolution contains a solid polymer electrolyte in accordance with any ofclaims 1 to
 7. 10. A membrane/electrode assembly for a solid polymerelectrolyte fuel cell comprising a polymer electrolyte membrane and agas diffusion electrode unit comprising a cathode and an anode which areplaced on both sides of said polymer electrolyte membrane, wherein saidpolymer electrolyte membrane is the polymer electrolyte membrane inaccordance with claim 8, said gas diffusion electrodes bind finecatalytic metal particles to the surfaces of a conductive material madeof carbon with a binder, and said binder is made of the polymerelectrolyte in accordance with claim
 9. 11. A solid polymer electrolytefuel cell comprising a polymer electrolyte membrane, a gas diffusionelectrode unit comprising a cathode and an anode which are placed onboth sides of said polymer electrolyte membrane, one pair of gasinpermeable separators which are provided to surround said gas diffusionelectrode unit, and one pair of current collecting members which areplaced between said solid polymer and said separator, wherein said solidpolymer electrolyte membrane is made of the polymer electrolyte membranein accordance with claim
 8. 12. A solid polymer electrolyte fuel cellcomprising a polymer electrolyte membrane, a gas diffusion electrodeunit comprising a cathode and an anode which are placed on both sides ofsaid polymer electrolyte membrane, one pair of gas inpermeableseparators which are provided to surround said gas diffusion electrodeunit, and one pair of current collecting members which are placedbetween said solid polymer and said separator, wherein said solidpolymer electrolyte membrane and said gas diffusion electrode are themembrane/electrode assembly in accordance with claim 10.